Abstract
Sigma factors of RNA polymerase can confer abilities for promoter recognition in transcription initiation. A cyanobacterium Synechocystis sp. strain PCC 6803 possesses nine sigma factor homologous genes (sig) assigned as group 1 (sigA), group 2 (sigB, sigC, sigD, sigE), and group 3 (sigF, sigG, sigH, sigI). Functions of the sigma factors have been revealed recently. For examples, SigB recognizes heat-shock and dark-induced gene promoters, SigD recognizes light-induced gene promoters, and SigC (SigB/SigE) recognizes nitrogen-related gene promoters, respectively. These group 2 sigma factors exist with the group 1 sigma factor SigA in the cells, and can cooperatively drive transcription from target promoters. The regulation may involve sigma factor replacements from SigA to SigB-SigE under some stress condition. We also would like to discuss a promoter recognized by a group 3 sigma factor. In this time, thus we will present a classification of promoter types for the sigma factors.
