Analyses will continue on the molecular features of regulation of gene expression by transcription attenuation in the trp operon of Enterobacteria, the trp operon of Bacilli, and the tryptophanase (tna) operon of E. coli. Each of theses examples involves different components and events, but the consequences of the regulatory decision is the same - determination whether or not transcription will be terminated at a site or sites in the leader region of the respective operon. Studies with the trp operon of Enterobacteria will focus on the mechanism of basal level control, and will involve analysis of ribosome release at the leader peptide stop codon, an assessment of the contributions of the alternative transcript hairpin structures, and an examination of the importance of the position of the transcribing polymerase at the moment the translating ribosome dissociates from the leader stop codon. In addition, several aspects of transcription pausing will be investigated, including the role of the antiterminator hairpin as a pause signal. The importance of the design of the leader peptide coding region also will be investigated. Studies on attenuation in the trp operon of Bacilli will concentrate on characterizing the regulatory gene, mtr, and its polypeptide product. The mechanism of action of this RNA binding regulatory protein will be determined; specifically Mtr's interaction with its target sequence in the leader transcript will be examined. Studies will be performed to verify the initial observation that during growth in excess tryptophan translation of the trpE coding region of the read through transcript is inhibited. Studies with the tna operon will concentrate on the role of the leader peptide and its translation in regulation of transcription termination at Rho factor- dependent termination sites in the distal segment of the leader region. A newly discovered locus that confers constitutive expression on the operon in trans, will be further characterized. Analyses will be performed to determine if tryptophan activation of a presumed antitermination protein renders the transcribing polymerase refractory to termination. Studies with these attenuation systems should reveal fundamental features of transcription, and transcriptional and translational control. In addition, attenuation in the B. subtilis trp operon may serve as a prokaryotic model for attenuation in higher organisms.
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