Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. This sigma factor is the primary sigma factor during exponential growth. Interacts transiently with the RNA polymerase catalytic core. Found in both the large cell variant (LCV) and small cell variant (SCV) stage (at protein level). LCVs are more metabolically active than SCVs. Belongs to the sigma-70 factor family. RpoD/SigA subfamily.