title: Sigma factors from E. coli, B. subtilis, phage SP01, and phage T4 are homologous proteins.
abstract: We show, using dot matrix comparisons and statistical analysis of sequence alignments, that seven sequenced sigma factors, E. coli sigma-70 and sigma-32, B. subtilis sigma-43 and sigma-29, phage SP01 gene products 28 and 34, and phage T4 gene product 55, comprise a homologous family of proteins. Sigma-70, sigma-32, and sigma-43 each have two copies of a sequence similar to the helix-turn-helix DNA binding motif seen in CRP, and lambda repressor and cro proteins. B. subtilis sigma-29, SP01 gp28, and SP01 gp34 have at least one copy similar to this sequence. We propose that a second sequence, conserved in all seven proteins is the core RNA polymerase binding site. A third region, present only in sigma-70 and sigma-43, may also be involved in interaction with core. Available mutational evidence supports our model for sigma factor structure.
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics*; D001435:Bacteriophages / Q000235:genetics*; D001665:Binding Sites; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D009154:Mutation; D011485:Protein Binding; D012808:Sigma Factor / Q000235:genetics*; D013045:Species Specificity; D013604:T-Phages / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D012808:Sigma Factor; D014157:Transcription Factors; D012321:DNA-Directed RNA Polymerases