Figure 1.

Staphylococcus aureus protein A (SPA) insertion in the β-subunit of E. coli RNAP. The primary sequence of the β-subunit is represented as a black bar. Evolutionarily conserved regions are shaded grey and labeled A–I (3). Evolutionarily hypervariable sequences are denoted by open, white boxes. Dispensable regions (DRI and DRII) are labeled, along with regions that have been deleted with little apparent consequence for basic RNAP assembly and transcription activity (black lines above sequence). The SPA insertion in DRII is shown. The sites of known rifampicin (rifampicin-resistant or Rif^R) mutations (6, 28) as well as split sites in archaebacterial genes and sites of cross-links to initiating nucleotide analogs (refs. 5 and 29; denoted as *) are also indicated.