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J. Bacteriol., 10 1995, 5554-5560, Vol 177, No. 19
BC Persson, GO Bylund, DE Berg and PM Wikstrom
We have analyzed the essentiality or contribution to growth of each of four
genes in the Escherichia coli trmD operon (rpsP, 21K, trmD, and rplS) and
of the flanking genes ffh and 16K by a reverse genetic method. Mutant
alleles were constructed in vitro on plasmids and transferred by
recombination to the corresponding lambda phage clone (lambda 439) and from
the phage clone to the E. coli chromosome. An ability to obtain
recombinants only in cells carrying a complementing plasmid indicated that
the mutated gene was essential, while an ability to obtain recombinants in
plasmid-free cells indicated nonessentiality. In this way, Ffh, the E. coli
homolog to the 54-kDa protein of the signal recognition particle of
mammalian cells, and ribosomal proteins S16 and L19 were shown to be
essential for viability. A deletion of the second gene, 21K, of the trmD
operon reduced the growth rate of the cells fivefold, indicating that the
wild-type 21-kDa protein is important for viability. A deletion-insertion
in the same gene resulted in the accumulation of an assembly intermediate
of the 50S ribosomal subunit, as a result of polar effects on the
expression of a downstream gene, rplS, which encodes ribosomal protein L19.
This finding suggests that L19, previously not considered to be an assembly
protein, contributes to the assembly of the 50S ribosomal subunits. Strains
deleted for the trmD gene, the third gene of the operon, encoding the tRNA
(m1G37)methyltransferase (or TrmD) showed a severalfold reduced growth
rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Functional analysis of the ffh-trmD region of the Escherichia coli chromosome by using reverse genetics
Department of Microbiology, University of Umea, Sweden.
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