Elizabeth J. Rogers

The cis‐effect of a nascent peptide on its translating ribosome: influence of the cat‐86 leader pentapeptide on translation termination at leader codon 6

Inducible cat genes from Gram‐positive bacteria are regulated by translation attenuation. The inducer chloramphenicol stalls a ribosome at a specific site in the leader of cat transcripts; this destabillzes a downstream stem‐loop structure that normally sequesters the ribosome‐binding site for the cat structural gene. The five‐amino‐acid peptide MVKTD that is synthesized when a ribosome has translated to the leader induction site is an inhibitor of peptidyl transferase In vitro. Thus, the peptide may be the in vivo determinant of the site of ribosome stalling. Here we provide evidence that the leader pentapeptide can exert a cis‐effect on its translating ribosome In vivo. Converting leader codon 6 to the ochre codon results in expression of cat‐86 in the absence of Inducer. We term this autoinduction. Autoinduction is abolished by mutations that change the amino‐acid sequence of the leader peptide but have no, or little, effect on the sequence of nucleotides at the leader stall site. In contrast, four nucleotide changes within the leader site occupied by the stalled ribosome that result in synonymous codon replacements do not diminish autoinduction. Our evidence indicates that the cat‐86 leader pentapeptide can alter the function of its translating ribosome.

The chloramphenicol-inducible catB gene in Agrobacterium tumefaciens is regulated by translation attenuation.

Agrobacterium tumefaciens strains C58, A136, and BG53 are chloramphenicol resistant, and each contains the catB gene originally identified by Tennigkeit and Matzuran (Gene 99:113-116, 1991). The chloramphenicol acetyltransferase activity in all of the strains is chloramphenicol inducible. Examination of the catB gene in strain BG53 indicates that it is regulated by an attenuation mechanism similar to translation attenuation that regulates inducible catA genes resident in gram-positive bacteria and the inducible cmlA gene that confers chloramphenicol resistance in Pseudomonas spp.