rpsL Mutations Research Articles

Mistranslation during phenylalanine starvation.

Starvation for phenylalanine led to leucine misincorporation frequencies of 0.1 and 0.6 at UUC codons in the argI transcript of Escherichia coli, but no detectable misincorporation at a UUU codon. Under similar starvation conditions the relative synthesis of full sized MS2 coat protein, encoded by the RNA virus or a DNA copy, is greatly reduced, preventing analysis of the protein. This reduction in amount is unaffected by a rpsL mutation.

The role of 2-methylthio-N6-isopentenyladenosine in readthrough and suppression of nonsense codons in Escherichia coli.

Readthrough and suppression of nonsense codons was compared in Escherichia coli strains with and without a miaA mutation, which confers a loss of the isopentenyladenosine modification in transfer RNA. Generally speaking, our results conform to predictions based on previous literature. In addition, we showed that the miaA mutation in strain TRPX is itself a UAA mutation. An antagonism between miaA and rpsL mutations, which confer streptomycin resistance, was also discovered. Our data further suggest that slight alterations of the translation apparatus are easily detectable by monitoring readthrough and suppression of nonsense codons. Our findings are discussed in the context of old and recent reports.

UGA suppressor that maps within a cluster of ribosomal protein genes.

A suppressor of UGA mutations (supU) maps near or within a cluster of ribosomal protein genes at 72 min on the Salmonella typhimurium genetic map. The suppressor is relatively inefficient, and its activity is abolished by rpsL (formerly strA) mutations. The suppressor is dominant to a wild-type supU allele. The map position of this suppressor suggests that it may owe its activity to an alteration of ribosome structure.

Adenosine 5'-triphosphate leakage does not cause abortive infection of bacteriophage T7 in male Escherichia coli.

galU and rpsL mutations restore plating efficiency of bacteriophage T7 in male Escherichia coli without suppressing leakage of adenosine 5'-triphosphate pools.

Formylation of initiator tRNA methionine in procaryotic protein synthesis: in vivo polarity in lactose operon expression.

Eucaryotic and procaryotic organisms differ in two aspects of their translation machinery: polycistronic messengers are expressed as a sequence of individual proteins only in procaryotes, and the initiation of protein synthesis proceeds with an initiator tRNA which is found to be modified (formylated) in procaryotes and not in eucaryotes. In the present study, we show that formylation is required in vivo for the coordinate expression of the Escherichia coli lactose operon. Our experiments are consistent with a translation mechanism using dissociated ribosomes at the 5' end of the mRNA in a reaction that is only weakly dependent on formylation at this initiation step; the ribosomes then travel along the messenger and can reinitiate after the intracistronic barrier without dissociation. This latter initiation step is strongly dependent on the level of formylation: a low level of the formyl group, obtained by the antifolic agent trimethoprim, induces a strong polarity in the expression of the lactose operon. There exist mutant strains in which this polarity is much less apparent than in the wild type. We show here that such is the case of rpsL mutants. Ribosomes mutated in the S12 protein (rpsL) are found to be much more easily dissociated than the wild type. This might explain why the expression of the lactose operon on rpsL strains remains coordinated when the intracellular level of formylation is decreased.