ALTERNATIVE PATTERNS OF HIS OPERON TRANSCRIPTION AND MESSENGER-RNA PROCESSING GENERATED BY METABOLIC PERTURBATION

Previous studies have shown that the expression of the his operon of S almonella typhimurium is regulated at the level of transcription initi ation, transcription elongation and RNA processing. We have analyzed h is RNA in both prototrophic strains or strains harboring regulatory an d auxotrophic mutations grown under a variety of metabolic conditions that lead to differential expression of the operon. Under some of thes e conditions, there is an increase in the amount of prematurely releas ed his-specific RNA, resulting in modulation of the relative amount of full-length transcripts. Under the same metabolic conditions, there i s also a modulation of RNA processing events that generate a very stab le RNA species comprising the five distal cistrons. These effects appe ar to be due to perturbation of the translation process caused by alte rations in the intracellular pool of initiator transfer RNA.