title: Expression of the leuX gene in Escherichia coli. Regulation at transcription and tRNA processing steps.
abstract: The leuX (supP) gene of Escherichia coli codes for a suppressor tRNA (tRNA(6Leu] that inserts leucine at the amber codon. Analysis of both in-vitro and in-vivo transcripts indicated that the gene is organized into a single gene operon, carrying its own promoter and rho-independent terminator, and its primary transcript accumulates in cells of wild-type E. coli with respect to tRNA processing. Systematic and quantitative measurements of both the unprocessed primary transcript and mature tRNA(Leu6) indicated that: (1) transcription of the leuX gene is under stringent control in vivo and is repressed in vitro by ppGpp; (2) transcription of the leuX gene is under growth rate-dependent control; but (3) the level of mature tRNA stays constant under various growth conditions. A model is proposed, which assumes that the enzyme catalyzing the first-step reaction in the leuX tRNA processing is limited, thereby keeping the level of mature tRNA(Leu6) at a constant level irrespective of changes in the level of the unprocessed primary transcript.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001483:Base Sequence; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D007930:Leucine / Q000235:genetics*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012322:RNA Precursors; D012323:RNA Processing, Post-Transcriptional; D012329:RNA, Bacterial / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*; D012356:RNA, Transfer, Leu / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D000596:Amino Acids; D004269:DNA, Bacterial; D012322:RNA Precursors; D012329:RNA, Bacterial; D012356:RNA, Transfer, Leu; D012343:RNA, Transfer; D007930:Leucine