MINIREVIEW Domain Architectures of 54-Dependent Transcriptional Activators

Transcription is the key control point for regulation of nu-merous cellular activities. Bacteria regulate levels of gene ex-pression by using transcription factors that modulate the re-cruitment of RNA polymerase (RNAP) to promoter elements in the DNA. Many bacteria also control gene expression by using a second class of transcription factor that uses energy from nucleotide hydrolysis to actively promote transcription initiation. The sigma () subunit is required for promoter recognition and initiation of transcription by the bacterial RNAP. Typically a bacterial cell may contain several alternative subunits with differing sequence specificities that direct the RNAP holoen-zyme to different sets of promoters. The 54 subunit (also known as RpoN, NtrA, and N) is unique (42) in that it shares no detectable homology with any of the other known sigm