Summary: In A3(2), two genes, and , encode the apparent polypeptide chain elongation factors EF-Tu1 and EF-Tu3, respectively. While appears to code for the major EF-Tu, the function of is unknown. To assess the role of EF-Tu3, was subjected to mutational and transcriptional analyses. Replacement of the 5′-half of by an antibiotic resistance cassette had no detectable effect on phenotype, indicating that is not essential for growth or differentiation. The transcription start site of was located approximately 195 nt upstream of the translation start site. The sequence of the promoter (P) resembles the consensus for the major class of eubacterial promoters, and P was recognized preferentially by an RNA polymerase fraction enriched in α, the principal . factor of . Nuclease S1 mapping failed to reveal transcripts during growth of in liquid culture, consistent with the apparent absence of EF-Tu3 in total protein extracts of the same strain. However, transcription was observed in cultures of M145 shortly after nutritional shiftdown (which resulted in the disappearance of ) and after addition of serine hydroxamate, both of which induce the stringent response. Transcription of was also observed in transition-phase and stationary-phase cultures of J1681, a strain deleted for (which specifies a tRNA for the rare leucine codon UUA). In all of these examples, transcription of followed the production of ppGpp, consistent with the hypothesis that is subject to positive stringent control.


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