Synthesis of the bacteriophage lambda P protein in amino acid-starved Escherichia coli cells

It was demonstrated previously that in isoleucine-starved Escherichia coli relA mutants harboring a plasmid derived from bacteriophage lambda the lambda O protein is not synthesized. However, a protein which coprecipited with the lambda O during immunoprecipitation with anti-lambda O serum was synthesized during the relaxed response. Here we found that this protein is the lambda P gene product. Despite significant inhibition of transcription from the pR promoter (which produces mRNA for the lambda P protein synthesis) during the stringent response, the lambda P protein was efficiently synthesized in relA- as well as relA+ strains starved for isoleucine, threonine and histidine, whereas the synthesis was negligible during starvation for arginine and leucine. The synthesis of the lambda P protein in amino acid-starved cells is sensitive to rifampicin. Thus we presume that this phenomenon is not caused by eventual increased stability of the lambda P mRNA but rather is an effect of preferential translation of this mRNA and incorporation of limited amount of amino acids arising in the starved cells as a result of intracellular proteolysis. One of possible explanations of the mechanism of this phenomenon may suggest that the same signals can be recognized in both prokaryotic and eukaryotic cells during initiation of translation at non-AUG codons.