Dependence of expression of an inducible Staphylococcus aureus cat gene on the translation of its leader sequence.

The gene for chloramphenicol (Cm) acetyltransferase (CAT) carried by the staphylococcal plasmid pUB112, whose expression can be stimulated by Cm, is preceded by a regulatory region containing two control elements. One of these consists of a Shine-Dalgarno (SD) sequence followed by an open reading frame coding for a leader peptide of nine amino acids. Previous work has shown that the SD sequence is essential for inducibility of Cm resistance by the antibiotic (Brückner and Matzura 1985). Here we demonstrate that fusion of the leader peptide coding sequence to a truncated 'lacZ gene results in synthesis of a leader peptide-beta-galactosidase fusion protein. Introduction of an ochre nonsense codon into the reading frame of the leader peptide sequence leads to considerable reduction of the basal expression and loss of inducibility of the cat gene. These results reveal that synthesis of the leader peptide is required for the basal and inducible expression of the cat gene and support the model of translational attenuation for its regulation.