Evidence that stdA, stdB, stdC, stdD, stdE, and stdF constitute a polycistronic transcriptional unit.

A. Diagram of the std operon. Opposite arrows below the diagram represent primer pairs used to examine co-transcription of contiguous coding sequences. B. Co-transcription of contiguous coding sequences in the std operon. PCR fragments generated with primer pairs specific for contiguous coding sequences were resolved in a 2% agarose gel, stained with ethidium bromide, and visualized with UV light. The 1 kb⁺ DNA ladder (Innovaplex, Sugar Land, TX) was used as size marker.