Comparative expression of the pC194 cat gene in Streptococcus pneumoniae, Bacillus subtilis and Escherichia coli

The expression of the cat gene of the staphylococcal plasmid pC194 present in the pLS1-pC194 composite plasmid pJS37 was lower in Streptococcus pneumoniae and Escherichia coli than in Bacillus subtilis. Different transcription start points (and, by inference, different promoter utilization) of the cat mRNA synthesized in S. pneumoniae or B. subtilis were detected. Plasmid pJS37 is prone to deletion formation when host cells are grown in the presence of chloramphenicol (Cm). The analysis of the expression of the cat gene carried by the deleted derivatives of pJS37 has shown that a new promoter for the synthesis of cat mRNA is involved in the selective advantage conferred to the host by those deleted plasmids. Characterization of either in vivo or in vitro deleted plasmids has shown that the nucleotide sequence that could encode for a putative leader peptide is required for the Cm-induced pC194 cat gene expression.