Jn. Li et Gr. Bjork, 1-METHYLGUANOSINE DEFICIENCY OF TRANSFER-RNA INFLUENCES COGNATE CODONINTERACTION AND METABOLISM IN SALMONELLA-TYPHIMURIUM, Journal of bacteriology, 177(22), 1995, pp. 6593-6600
1-Methylguanosine (m(1)G) is present next to the 3' end of the anticod
on (position 37) tRNA(1,2,3)(Leu),tRNA(1,2,3)(Pro), and tRNA(3)(Arg).
A mutant of Salmonella typhimurium lacks m(1)G in these seven tRNAs wh
en grown at or above 37 degrees C, as a result of a mutation (trmD3) i
n the structural gene (trmD) for the tRNA(m(1)G37) methyltransferase.
The m(1)G deficiency induced 24 and 26% reductions in the growth rate
and polypeptide chain elongation rate, respectively, in morpholineprop
anesulfonic acid (MOPS)-glucose minimal medium at 37 degrees C. The ex
pression of the leuABCD operon is controlled by the rate with which tR
NA(2)(Leu) and tRNA(3)(Leu) read four leucine codons in the leu-leader
mRNA, Lack of m(1)G in these tRNAs did not influence the expression o
f this operon, suggesting that m(1)G did not influence the efficiency
of tRNA(2,3)(Leu). Since the average step time of the m(1)G-deficient
tRNAs was 2,3' increased 3.3-fold, the results suggest that the impact
of m(1)G in decoding cognate codons may be tRNA dependent, The trmD3
mutation rendered the cell more resistant or sensitive to several amin
o acid analogs, 3-Nitro-L-tyrosine (NT), to which the trmD3 mutant is
sensitive, was shown to be transported by the tryptophan-specific perm
ease, 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 involv
ed in the metabolic reactions affected by the analog, Our results also
suggest that tRNA modification may be a regulatory device for gene ex
pression.