<jats:title>ABSTRACT</jats:title> <jats:p> A polycistronic transcript that is initiated at the <jats:italic>lat</jats:italic> promoter has been implicated in the expression of the genes involved in early steps of cephamycin C biosynthesis in <jats:italic>Streptomyces clavuligerus. pcbC</jats:italic> is also expressed as a monocistronic transcript from its own promoter. However, an alternative interpretation involving expression via three separate yet interdependent transcripts has also been proposed. To distinguish between these possibilities, mutants lacking the <jats:italic>lat</jats:italic> promoter and containing a transcription terminator within the <jats:italic>lat</jats:italic> gene (Δ <jats:italic>lat</jats:italic> :: <jats:italic>tsr</jats:italic> /term mutants) were created. This mutation eliminated the production of lysine-ɛ-aminotransferase (the <jats:italic>lat</jats:italic> gene product) but also affected the expression of downstream genes, indicating an operon arrangement. Production of δ-( <jats:sc>l</jats:sc> -α-aminoadipyl)- <jats:sc>l</jats:sc> -cysteinyl- <jats:sc>d</jats:sc> -valine synthetase (ACVS) (the <jats:italic>pcbAB</jats:italic> gene product) was eliminated in Δ <jats:italic>lat</jats:italic> :: <jats:italic>tsr</jats:italic> /term mutants, while production of isopenicillin N synthase (IPNS) (the <jats:italic>pcbC</jats:italic> gene product) was greatly reduced. The provision of α-aminoadipate to the Δ <jats:italic>lat</jats:italic> :: <jats:italic>tsr</jats:italic> /term mutants, either via exogenous feeding or via <jats:italic>lat</jats:italic> gene complementation, did not restore production of ACVS or IPNS. Analysis of RNA isolated from the Δ <jats:italic>lat</jats:italic> :: <jats:italic>tsr</jats:italic> /term mutants confirmed that the polycistronic transcript was absent but also indicated that monocistronic <jats:italic>pcbC</jats:italic> transcript levels were greatly decreased. In contrast, Δ <jats:italic>lat</jats:italic> mutants created by in-frame internal deletion of <jats:italic>lat</jats:italic> maintained the polycistronic transcript and allowed production of wild-type levels of both ACVS and IPNS.