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J. Bacteriol., 11 1995, 6593-6600, Vol 177, No. 22
JN Li and GR Bjork
1-Methylguanosine (m1G) is present next to the 3' end of the anticodon
(position 37) in tRNA(1,2,3,Leu), tRNA(1,2,3,Pro), and tRNA(3Arg). A mutant
of Salmonella typhimurium lacks m1G in these seven tRNAs when grown at or
above 37 degrees C, as a result of a mutation (trmD3) in the structural
gene (trmD) for the tRNA(m1G37)methyltransferase. The m1G deficiency
induced 24 and 26% reductions in the growth rate and polypeptide chain
elongation rate, respectively, in morpholinepropanesulfonic acid
(MOPS)-glucose minimal medium at 37 degrees C. The expression of the
leuABCD operon is controlled by the rate with which tRNA(2Leu) and
tRNA(3Leu) read four leucine codons in the leu-leader mRNA. Lack of m1G in
these tRNAs did not influence the expression of this operon, suggesting
that m1G did not influence the efficiency of tRNA(2,3Leu). Since the
average step time of the m1G- deficient tRNAs was increased 3.3-fold, the
results suggest that the impact of m1G in decoding cognate codons may be
tRNA dependent. The trmD3 mutation rendered the cell more resistant or
sensitive to several amino acid analogs. 3-Nitro-L-tyrosine (NT), to which
the trmD3 mutant is sensitive, was shown to be transported by the
tryptophan-specific permease, and mutations in this gene (mtr) render the
cell resistant to NT. Since the trmD3 mutation did not affect the activity
of the permease, some internal metabolic step(s), but not the uptake of the
analog per se, is affected. We suggest that the trmD3-mediated NT
sensitivity is by an abnormal translation of some mRNA(s) whose product(s)
is involved in the metabolic reactions affected by the analog.(ABSTRACT
TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
1-Methylguanosine deficiency of tRNA influences cognate codon interaction and metabolism in Salmonella typhimurium
Department of Microbiology, Umea University, Sweden.
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