A majority of Rhodobacter sphaeroides promoters lack a crucial RNA polymerase recognition feature, enabling coordinated transcription activation

Bacterial promoters are often predicted by similarity to the Escherichia coli −10 and −35 consensus elements. Although these elements are highly conserved in diverse bacterial phyla, only 30 to 43% of promoters we analyzed from Rhodobacter sphaeroides and two other α-proteobacteria contained −7T, a base in the −10 element present in 90 to 99% of promoters from non–α-proteobacteria. Expression from 15 of 16 R. sphaeroides promoters tested in vitro that lacked −7T was very weak, but we identified an essential transcription factor, CarD, that activated all 15 of these promoters. We suggest that promoters lacking a critical base in a consensus element can shape the transcriptome by coordinating expression of large numbers of genes by a single transcription factor.