Division of Infectious Diseases, Department
of Medicine, Vanderbilt University School of Medicine and VA
Medical Center, Nashville, Tennessee,1 and
First Department of Internal Medicine, Nagoya University
School of Medicine, Nagoya, Japan2
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INTRODUCTION |
Helicobacter pylori, a
microaerophilic, gram-negative bacterium that colonizes the human
stomach, has been recognized as the major causative agent of chronic
gastritis and as playing a role in peptic ulcer disease and gastric
cancer (8). H. pylori strains have a high degree
of diversity at the genetic level (2, 19, 34), including a
high rate of point mutations in conserved genes such as ureB
(28) and flaA (45), mosaicism within
genes such as vacA (5), and the presence of
nonconserved DNA fragments, in particular, the cag
pathogenicity island (2, 10, 13, 50). Other factors that
lead to further diversity among H. pylori strains are the
presence of insertion sequences (10, 23) or plasmids
(31), variation in gene order (25), and the
complement of putative restriction endonucleases (2, 48).
The genetic diversity of H. pylori has clinical
significance, since markers for strains with enhanced virulence have
been identified (5, 13, 39, 50). Additionally, techniques such as restriction fragment length polymorphism and randomly amplified
polymorphic DNA PCR have been used to exploit this heterogeneity for
epidemiologic purpose (2, 3, 41, 51).
Horizontal DNA transfer within the reservoir for H. pylori,
i.e., the stomach of primates, would contribute to the development of
genetic diversity (33). There is substantial evidence that recombination among H. pylori strains has been an important
feature of their evolution (5, 23, 46). Natural
transformation in bacteria is a complex process involving DNA binding,
uptake/translocation, and recombination. Many H. pylori
strains are known to be naturally competent for transformation in vitro
(32, 37, 43, 49, 55). However, the mechanisms for
transformation of DNA have not been closely studied for H. pylori. Thus far, only recA (44, 47) and the
comB locus (22) have been identified as having a
role in H. pylori transformation. Recognition of the
mechanisms involved in genetic exchange may help us to understand the
adaptation of H. pylori to changing environments and could
shed light on clinically important issues of virulence and development
of antibiotic resistance (7, 21, 52). The complete genomic
sequence of H. pylori 26695 (48) revealed a
810-bp open reading frame (ORF) (HP0333) encoding a deduced protein of
270 amino acids (30,470-Da molecular mass) with homology to DprA
(encoded by dprA) of Haemophilus influenzae. In
H. influenzae, dprA is required for
transformation by chromosomal DNA (29). We therefore sought
to determine whether HP0333 is required for natural transformation in
H. pylori.
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MATERIALS AND METHODS |
Strains and growth conditions.
Strains and plasmids used in
this study are listed in Table 1.
Escherichia coli was routinely grown at 37°C in
Luria-Bertani broth or agar supplemented with ampicillin (100 µg/ml),
kanamycin (25 µg/ml), and/or chloramphenicol (60 µg/ml), when
appropriate. H. pylori strains were grown on Trypticase soy
agar (TSA) with 5% sheep blood (BBL) or Brucella-serum
(BS;BBL) agar with 10% newborn calf serum (Intergen) plates at 37°C
in a 5% CO2 atmosphere. Antibiotic-resistant H. pylori transformants were selected with kanamycin (25 µg/ml),
chloramphenicol (10 µg/ml), streptomycin (20 µg/ml), or
spectinomycin (20 µg/ml). We selected H. pylori strains
that were spontaneously streptomycin or spectinomycin resistant
(Strr or Spcr) by plating large numbers
(approximately 1010) of bacteria on TSA medium containing
streptomycin (10 µg/ml) or spectinomycin (10 µg/ml), respectively.
Construction of plasmids and strains.
The HP0333 ORF of
strain 26695 (48) was amplified by PCR using primers A9853
and A9854. The product was ligated into pGEM-T Easy and transformed
into E. coli DH5
. A unique BamHI site was created by inverse PCR with primers C3581 and C3582. Plasmid pUC4K was
digested with BamHI, after which the kanamycin resistance (Kanr; aphA) cassette was isolated by agarose
gel electrophoresis and ligated into the inverse PCR product to disrupt
the HP0333 ORF, creating pDPR2. H. pylori 84-183 and HPK5
were transformed to Kanr with pDPR2, to create
84-183/0333::aphA and
HPK5/0333::aphA, respectively. Chromosomal DNA was
isolated from strains 84-183, HPK5,
84-183/0333::aphA, and
HPK5/0333::aphA, and the insertion of the
aphA cassette within HP0333 in the transformants was
confirmed by PCR using primer pairs C3635-C3636, C3635-C3632, and
C3634-C3636. PCR oligonucleotide primers specific for HP0333 or
aphA were used, and the sizes of the PCR products were
evaluated by agarose gel electrophoresis (Table
2).
Electroporation.
HPK5 was transformed with pHP1 by
electroporation as described elsewhere (32), resulting in
strain 98-716 (Table 1).
DNA techniques and sequence analysis.
Standard molecular
techniques were used (42). H. pylori chromosomal
DNA was prepared from cells of each strain after 48 h of growth on
two agar plates as described previously (56). Plasmid DNA
was prepared from H. pylori after 48 h of growth or from E. coli after overnight cultures, using a midi-prep
protocol (Qiagen Inc., Valencia, Calif.) according to the
manufacturer's instructions. Database similarity searches of GenBank
and Unfinished Microbial Genome sequences were done with the BLAST
algorithms (4). Sequence comparisons was performed with
Genetics Computer Group analysis programs (5). Secondary
structure analysis was done by the Chou-Fasman algorithm
(12), using the program Peptidestructure (24).
Further analysis of predicted protein sequences was done with PAUP 3.1 (Smithsonian Institution, Washington, D.C.), MacClade version 3 (35), Phylip (17), and TreeView (38).
Natural transformation.
Recipient H. pylori cells
were harvested from 48-h growth on one agar plate into 1 ml of
phosphate-buffered saline (PBS) and then centrifuged at 8,500 g for 5 min. The pellet was resuspended in 300 µl of PBS.
Each transformation mixture, consisting of 25 µl of recipient cells
and 30 ng of donor DNA, was spotted onto a TSA plate (approximately 20 ng of DNA/25 µl of cells is a saturating amount of DNA [data not
shown]). Plates were incubated overnight at 37°C in a 5%
CO2 atmosphere. After 18 h of incubation, the transformation mixture was harvested into 1 ml of PBS, and 100-µl aliquots of appropriate serial dilutions were plated on BS-streptomycin or BS-spectinomycin plates and on TSA plates. All plates were incubated
for 4 days at 37°C in a 5% CO2 atmosphere, after which transformants and total viable cells were counted. The transformation frequency was determined by the number of Strr or
Spcr colonies per microgram of DNA per recipient CFU.
Analyses of complementation.
Portions of the H. pylori urease operon (ureAB) and its promoter region
(Pure) were amplified from strain 26695 by PCR
using primers described in Table 2, and these products were ligated
into pUC19. HP0333 was amplified from chromosomal DNA from strain 26695 and ligated between Pure and ureAB. The cat cassette was isolated from pBSC103 by digestion with
SmaI and EcoRV, purified, and ligated between
HP0333 and ureAB to create pANDO2. HPK5 was transformed with
pANDO2, resulting in C5. C5 was transformed by pDPR2 to create C5G9 and
C5G10. The frequency of natural transformation was compared for the
wild-type strain HPK5 and its isogenic mutants,
HPK5/0333::aphA, C5, C5G9, and C5G10 (see Fig. 5).
| |
RESULTS |
Comparison of H. pylori HP0333 with other bacterial
sequences.
Comparison of the predicted product of HP0333 from
strain 26695 with the genomic sequence of strain J99 (3)
revealed a homolog (JHP316) with 93.7% nucleotide identity and 95.9%
amino acid identity. HP0333 is predicted to encode a protein with 270 amino acids, while JHP316 is predicted to encode a protein of 266 amino
acids. We next sought to determine whether the predicted product of
HP0333 had homology to proteins other than DprA of H. influenzae. A BLAST search of GenBank and Unfinished Microbial Genome sequences with the HP0333 predicted protein sequence revealed strong homology (P = 4 × 10
53 to
3 × 105) with predicted proteins from 24 different
bacterial species, including H. influenzae (P = 5 × 1015). Of the 24 completed and annotated
genomes searched (from 22 species), homologs were found in 15 (13 species) (Fig. 1). These species included
both gram-negative and gram-positive bacteria, as well as an archaeal
organism, Pyrococcus furiosus (data not shown). Of these
organisms, only six, H. pylori, Campylobacter jejuni, Bacillus subtilis, Streptococcus
pneumoniae, H. influenzae, and Neisseria
gonorrhoeae, are known to be naturally competent (Fig. 1). No
homologs were identified in Archaeoglobus fulgidus, Rickettsia prowazekii, Chlamydia pneumoniae,
Chlamydia trachomatis, Methanobacterium
thermoautotrophicum, Methanococcus jannaschii, or
Pyrococcus horikoshii, for which the complete genome
sequences are available. This indicates that DprA is not universally
present in bacteria. In addition, homologs were identified in 14 strains (14 species) for which partial genome data are available. The proteins for which complete sequences are available are predicted to
vary in size from 240 (C. jejuni) to 398 amino acids
(Synechocystis and N. gonorrhoeae). The strongest
homology was to a predicted protein from C. jejuni (Cj0634;
P = 4 × 1053), and phylogenetic
analysis also indicates that these sequences are closely related (Fig.
1). As expected, other homologs that are closely related to one another
are from S. pneumoniae and Streptococcus
pyogenes, from two members of the family
Enterobacteriaceae (E. coli and Salmonella
typhi), and from Mycobacterium tuberculosis, Rhodococcus fascians, and Streptomyces
coelicolor.
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FIG. 1.
Phylogram showing relatedness of putative proteins with
homology to HP0333. Organisms in which related putative proteins were
found are indicated. GenBank accession numbers for complete DNA
sequence submissions are as follows: H. influenzae, U18657;
Synchocystis, D90905; B. subtilis, Z99112;
M. tuberculosis, Z74024; S. coelicolor, AL023797;
B. burgdorferi, AE001137; E. coli, X65946;
T. pallidum, AE001217; S. aureus AB015195; and
A. aeolicus AE000728. Sequences from unfinished microbial
genomes are from the following databases: C. jejuni, The
Sanger Centre (42a); C. tepidum, The Institute
for Genomic Research (TIGR) (23a); Y. pestis, The
Sanger Centre; N. gonorrhoeae, University of Oklahoma's
Advanced Center for Genome Technology (OU-AGCT) (1);
P. gingivalis, TIGR; D. radiodurans, TIGR;
A. actinomycetemcomitans, OU-AGCT; S. pneumoniae,
TIGR; P. aeruginosa, Pseudomonas Genome Project
(40a); S. pyogenes, OU-AGCT; S. typhi,
The Sanger Centre; E. faecalis, TIGR; T. maritima, TIGR. The accession number for the R. fascians homolog is AF001836.
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When the sequences of these predicted proteins were aligned, a region
of 193 residues including amino acids 17 to 201 of HP0333 was found to
be highly similar among all of the proteins (Fig. 2). Of the 210 positions, 80 (38.1%)
were conserved in at least 60% of the sequences and an additional 22 (10.5%) positions had conservative substitutions, for a total of
48.6% similar residues. Within this region, there are three areas of
high relatedness. Amino acids 47 to 60 (relative to the consensus
sequence) have 53.8% identity (76.9% similarity), amino acids 75 to
120 have 61.0% identity (68.3% similarity), and amino acids 152 to
200 have 59.6% identity (78.7% similarity). As expected, secondary structure predictions of the putative proteins from H. pylori, H. influenzae, and C. jejuni show
similarity within the region of amino acid sequence homology, including
many potential turns (data not shown). In total, these data indicate
that HP0333 belongs to a family of genes conserved among many, but not
all, known bacterial genera.
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FIG. 2.
Multiple sequence alignment of predicted H. pylori HP0333 product and 24 homologs. Alignment includes region
of conservation between HP0333 product and proteins identified by BLAST
search. Consensus amino acids, i.e., those which are conserved among
greater than 60% of the sequences, are indicated by black boxes (and
the corresponding amino acids on the consensus line), whereas gray
boxes (and a + on the consensus line) indicate similar amino
acids. Alignment was performed with the Genetics Computer Group program
Pileup and shaded with MacBoxshade.
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Construction of HP0333 H. pylori mutants.
To study
the function of HP0333, which we hypothesized to be involved in the
natural competence of H. pylori, we constructed mutants of
strains HPK5 and 84-183 in which there is an aphA insertion in the HP0333 ORF. First, HP0333 was PCR amplified by using primers based on HP0333 from strain 26695 and then cloned in pGEM-T Easy. A
unique BamHI site within HP0333 was created by inverse PCR, and the aphA cassette was ligated into this product,
disrupting the HP0333 ORF, resulting in pDPR2. When wild-type H. pylori strains were transformed to Kanr with pDPR2,
the frequencies of transformation were 2.2 × 1010
transformants/µg of DNA/CFU for 84-183 and 1.1 × 106 transformants/µg of DNA/CFU for HPK5. PCR with
HP0333 and aphA-specific primers confirmed the correct
replacement of HP0333 with HP0333::aphA by allelic
exchange (Fig. 3). The colony morphology
and growth on TSA plates of the HP0333::aphA
mutants appeared unchanged from their wild-type parental strains.
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FIG. 3.
Map of the region of HP0332 to HP0334 showing PCR
primers in relation to HP0333 and the inserted aphA
cassette.
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Ability of wild-type H. pylori and HP0333 mutants to be
transformed by H. pylori chromosomal DNA.
To examine
whether disruption of HP0333 affected the ability of H. pylori cells to be transformed by H. pylori chromosomal DNA, we used chromosomal DNA from Strr or Spcr
strains as the donor DNA to determine the effect of HP0333 disruption on transformation frequency (Table 3).
Neither the source of the donor DNA nor the antibiotic resistance
marker used had any significant effect on transformation frequency
(Table 3). The median frequencies of transformation of the wild-type
H. pylori strains to Strr or Spcr
were 4.1 × 104 transformants/µg of DNA/CFU for
84-183 and 5.4 × 104 transformants/µg of
DNA/recipient CFU for HPK5. In contrast, the median frequencies of
transformation of the mutant H. pylori strains were 2.0 × 107/µg of DNA/CFU for
84-183/0333::aphA and 6.7 × 106/µg of DNA/CFU for
HPK5/0333::aphA (Table 3). Thus, disruption of
HP0333 substantially reduced (medians of 3.3 log10 for
84-183 and 1.9 log10 for HPK5) but did not eliminate
H. pylori transformation for either strain.
Genetic characterization of the HP0333 locus.
In H. pylori 26695, HP0333 is flanked by three predicted genes upstream
(ilvC, minD, and minE homologs) and
several ORFs downstream that could represent an operon. We examined 11 H. pylori strains to determine whether HP0333 was
universally present. By PCR using primers C3635 and C3636, all 11 strains had the expected 939-bp product, indicating that HP0333 was
conserved (data not shown). We next examined whether the locus of
HP0333 in the wild-type strains that we studied was similar (Fig.
4). A series of PCRs involving HP0333 and
its flanking genes indicated essentially identical organization of this
locus in three strains studied. Only the PCR involving HP0334 and
HP0335 showed any heterogeneity. Sequence analysis of the PCR products
from strains 26695 and 84-183 revealed a 53-bp deletion in strain
84-183 between ORFs HP0334 and HP0335 relative to strain 26695 (data
not shown). In strain J99, ilvC, minD, and
minE homologs also are present upstream of JHP316, the
dprA homolog. Because of this conservation of gene order
suggestive of a polycistronic operon, we sought to examine the function
of HP0333 in isolation from its flanking genes.
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FIG. 4.
Conservation of chromosomal organization flanking HP0333
in three H. pylori strains. (A) Map of 4.7-kb region from
nadE (HP0329) through HP0335 in strain 26695. Arrowheads
refer to PCR primers (Table 2); arrows reflect the direction of
transcription. (B) Products of PCR using these primer pairs for strains
84-183 (lanes 1), HPK5 (lanes 2), and 26695 (lanes 3). Lanes 4 are
no-DNA controls.
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Complementation analyses.
To confirm that the decreased
transformation frequency of the mutants is due to loss of HP0333 and
not due to a polar effect on downstream genes, we sought to complement
the mutation. To restore HPK5/0333::aphA
to a wild-type phenotype, we developed a strategy to integrate HP0333
into the H. pylori chromosome downstream of the
ureAB promoter (Fig. 5).
First, we cloned a fragment of the ureAB locus into pUC19
and then sequentially introduced HP0333 and cat to create
pANDO2. Then, H. pylori HPK5 was transformed with pANDO2,
resulting in strain C5, in which HP0333 is expressed from the native
ureAB promoter (Table 1; Fig. 5). Next we transformed strain
C5 with pDPR2, which disrupted either the ORF of HP0333 or the copy of
HP0333 in the ureAB locus, to create strain C5G9 or C5G10,
respectively (Table 1; Fig. 5). The identity of each of these mutants
was confirmed by specific PCRs (data not shown). We then tested the
wild-type strain HPK5 and its derivatives, HPK5/0333::aphA, C5, C5G9, and C5G10, for
the ability to be transformed by homologous chromosomal DNA from a
Strr strain (Table 4). In
strain C5G9, with HP0333 in the ureAB locus, the frequency
of transformation was completely restored to that of the wild-type
strain HPK5. That the decrease in transformability by an insertion
within HP0333 could be complemented by HP0333 in trans
indicates that the loss of phenotype in
HPK5/0333::aphA was not due to a polar effect on
downstream genes. Additionally, the transformation frequency was not
increased compared to the wild-type strain when two intact copies of
HP0333 were present in strain C5 (Table 4).
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FIG. 5.
Construction of H. pylori mutants involving
HP0333. For each strain, the loci surrounding HP0333 and
ureAB are shown. A Kanr (aphA)
cassette was introduced into HP0333 of HPK5 to create
HPK5/0333::aphA. The insert of pANDO2 was
introduced into the ureAB locus of HPK5 downstream of the
ureAB promoter (Pure) to create C5.
An aphA cassette was introduced into strain C5 to create
either C5G9 or C5G10.
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Efficiency of transformation of the wild-type H. pylori
strains and mutants by plasmid DNA.
In H. influenzae,
dprA is necessary for uptake of chromosomal but not plasmid
DNA (29). Using HPK5 and its mutant derivatives, we sought
to examine the role of HP0333 in uptake of a plasmid that does not
integrate into the bacterial chromosome. The strains were examined for
competence by natural transformation with plasmid pHP1HPK5,
which carries an ampicillin resistance (Ampr;
bla) marker. The frequency of transformation of the
wild-type H. pylori strain HPK5 to Ampr was
4.9 × 105/µg of DNA/CFU, and that of
HPK5/0333::aphA strain was less than 5.1 × 107/µg of DNA/recipient CFU (Table
5). Complementation with HP0333 in
trans in strain C5G9 restored the wild-type phenotype. Thus, mutation in HP0333 also was shown to result in a marked decrease (>1.9
log10) in transformation by plasmid DNA.
| |
DISCUSSION |
From the strong homology of the HP0333 product with predicted
proteins from diverse bacterial genera, it is clear that the HP0333
product belongs to a family of bacterial proteins that, although their
exact biochemical function is not known, has been shown to be involved
in DNA transformation in two naturally competent organisms: H. influenzae (29) and now H. pylori. The first
member of this family described was smf of E. coli; however, no function was identified (36).
Although these proteins are conserved among many gram-negative and
gram-positive organisms, homologs are not present in a number of
archaea, including A. fulgidus, M. thermoautotrophicum, and P. horikoshii. However, the
presence of a homolog in P. furiosus indicates that it is
not exclusively a eubacterial protein. Additionally, obligate
intracellular organisms with small genomes, such as C. trachomatis, M. genitalium, M. pneumoniae,
and R. prowazekii, do not appear to have homologs,
suggesting that this protein is not a part of the minimal complement
required by bacteria. Analysis of the predicted proteins indicates
close relationships, as expected, between organisms known to have
similar phylogenies (Fig. 1). The wide distribution, conserved
sequence, and this phylogenetic pattern imply an ancient origin and an
important function. Based on the first protein for which a function was
ascribed (29), we provisionally call this the DprA family.
Similarity of the predicted secondary structures for the
dprA homologs from H. pylori, C. jejuni, and H. influenzae also suggest a close
functional relationship between these proteins.
Many H. pylori strains are highly competent for
transformation by chromosomal DNA (32, 37, 49, 55). The
presence of colonization of humans by more than one strain is common
(11, 26, 53), and the strongly recombinational population
structure of H. pylori (20, 46) suggests that
horizontal gene transfer is a frequent event. In wild-type strains,
transformation by homologous DNA was no more frequent than by DNA from
a heterologous H. pylori strain. This observation implies
that there are not substantial restriction barriers for H. pylori uptake of native chromosomal DNA. Thus, the existence of
specialized mechanisms to permit DNA uptake and incorporation by
H. pylori may be postulated. In H. influenzae and
S. pneumoniae, two other naturally competent bacteria, dprA and cilB (dprA homolog),
respectively, are required for transformation by chromosomal DNA
(9, 29). Since the genomes of H. pylori strains
26695 and J99 contain a dprA homolog (ORFs HP0333 and JHP316, respectively) (3, 48), we sought to examine its role in the transformation of H. pylori.
The presence of HP0333 in all 11 strains studied and its invariant
relationship to flanking genes suggest a conserved function within
H. pylori. That disruption of HP0333 markedly reduced the transformation of H. pylori strains by chromosomal DNA
supports our hypothesis. These findings are not due to a polar effect, since complementation with HP0333 in trans restored the
wild-type phenotype. Thus, HP0333 has a dprA function and
might appropriately be called H. pylori dprA. Additionally,
the complementation studies showed that having two functional copies of
dprA does not enhance transformation; therefore, other steps
in DNA transformation must be rate limiting.
Natural transformation is believed to involve three sequential steps:
binding, uptake/translocation, and recombination. For H. influenzae dprA, mutational analysis (29) showed that
its role occurred after binding, being involved in DNA translocation into the cytoplasm and/or recombination. Based on the strong homology of the central regions of the dprA from H. influenzae and H. pylori, we speculate that a similar
step may be involved, but this has not yet been studied directly.
Although H. pylori and H. influenzae dprA have
similar functions, there are important differences. As with H. influenzae, dprA disruption in H. pylori
substantially reduced, but did not eliminate, transformation. However,
dprA disruption in H. influenzae reduced the
transformation frequency 10,000-fold (29), whereas in
H. pylori the disruption of HP0333 resulted in only a
100-fold decrease in transformation frequency. Thus,
dprA-independent mechanisms of transformation probably exist
in H. pylori. In H. influenzae, dprA,
while necessary for transformation by chromosomal DNA, is not necessary
for plasmid DNA (29). In contrast, disruption of HP0333
completely eliminated H. pylori transformation by plasmid DNA. Considering the three-step model presented above, transformation by chromosomal or plasmid DNA potentially share the first two steps,
but recombination is not required for transformation by plasmid DNA in
all organisms. Our data therefore suggest that the shared H. pylori dprA function occurs during the first two steps. Since
binding to the bacterial cell may not be involved, the remaining step
is uptake/translocation. For H. influenzae, both chromosomal
and plasmid DNA are initially taken up into the transformasome as
double-stranded DNA (6, 16, 27, 40). Although we do not know
the mechanism by which H. pylori takes up chromosomal or
plasmid DNA, it is possible that the mechanism is different from the
H. influenzae model.
The genes upstream of dprA in H. pylori, homologs
of minD, minE, and ilvC, are not
present in the same locus in H. influenzae. In H. influenzae dprA (HI0985) and ilvC (HI0682) are located
far apart on the chromosome, and minD and minE
are not present. minD and minE are involved in
cell division in E. coli (14), while ilvC is required for isoleucine and valine synthesis
(1). The function of the putative operon containing
dprA, homologs of these three genes (ilvC,
minD, and minE), and 13 other ORFs with unknown homologs is not yet apparent. The organization of dprA in
relation to its flanking genes in 26695 (48) and J99
(3) appears conserved in the two other strains tested,
suggesting that in all those strains dprA may be part of a
polycistronic operon. Like dprA in H. influenzae,
the genes flanking H. pylori dprA are homologous to
metabolic genes or those for which no function is known. For H. influenzae, it is unclear whether the genes downstream of
dprA are required for transformation. Karudapuram and Barcak
showed the dprA and the downstream dprB and
dprC are transcriptionally coregulated and competence
inducible (30). However, our complementation studies show
H. pylori dprA, by itself, is sufficient to restore the full
wild-type phenotype. Therefore, the flanking genes, even if they are
cotranscribed, are not required for the full transformation event.
Although H. influenzae, S. pneumoniae, and
H. pylori are naturally competent for DNA transformation,
and their DprA homologs play a role in uptake, the function of other
DprA family members, which are present in species that are not
naturally competent, is unknown. Based on its role in H. influenzae, S. pneumoniae, and H. pylori, we
speculate that DprA may be a DNA-processing protein.
This work was supported in part by grant R01-DK53707 from the National
Institutes of Health and by the Medical Research Service of the
Department of Veterans Affairs.
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Abstract
Introduction
