Previous Article | Next Article ![]()
Journal of Bacteriology, November 1998, p. 5639-5645, Vol. 180, No. 21
Genetik, Fachbereich Biologie,
Universität Oldenburg, D-26111 Oldenburg, Germany
Received 22 June 1998/Accepted 2 September 1998
The RecBCD enzyme has a powerful duplex DNA exonuclease activity in
vivo. We found that this activity decreased strongly when cells were
irradiated with UV light (135 J/m2). The activity decrease
was seen by an increase in survival of phage T4
2
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Interaction of RecBCD Enzyme with DNA at
Double-Strand Breaks Produced in UV-Irradiated Escherichia
coli: Requirement for DNA End Processing
of about 200-fold (phage T4
2
has defective duplex DNA end-protecting
gene 2 protein). The activity decrease depended on excision
repair proficiency of the cells and a postirradiation incubation.
During this time, chromosome fragmentation occurred as demonstrated by
pulsed-field gel electrophoresis. In accord with previous observations,
it was concluded that the RecBCD enzyme is silenced during interaction
with duplex DNA fragments containing Chi nucleotide sequences. The
silencing was suppressed by induction or permanent derepression of the
SOS system or by the overproduction of single-strand DNA binding
protein (from a plasmid with ssb+) which is
known to inhibit degradation of chromosomal DNA by cellular DNases.
Further, mutations in xonA, recJ, and
sbcCD, particularly in the recJ sbcCD and
xonA recJ sbcCD combinations, impeded RecBCD silencing. The
findings suggest that the DNA fragments had single-stranded tails of a
length which prevents loading of RecBCD. It is concluded that in
wild-type cells the tails are effectively removed by
single-strand-specific DNases including exonuclease I, RecJ DNase, and
SbcCD DNase. By this, tailed DNA ends are processed to entry sites for
RecBCD. It is proposed that end blunting functions to direct DNA ends
into the RecABCD pathway. This pathway specifically activates
Chi-containing regions for recombination and recombinational repair.
*
Corresponding author. Mailing address: Genetik,
Fachbereich Biologie, Universität Oldenburg, Postfach 2503, D-26111 Oldenburg, Germany. Phone: 49-441-798 3298. Fax: 49-441-798 3298 or 49-441-798 3250. E-mail:
genetics{at}biologie.uni-oldenburg.de.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»