title: Transient association of an alternative sigma factor, ComX, with RNA polymerase during the period of competence for genetic transformation in Streptococcus pneumoniae.
abstract: Natural transformation in Streptococcus pneumoniae is regulated by a quorum-sensing system that acts through accumulation and sensing of a peptide pheromone (competence-stimulating peptide [CSP]) to control many competence-specific genes acting in DNA uptake, processing, and integration. The period of competence induced by CSP lasts only 15 min (quarter-height peak width). The recently identified regulator ComX is required for the CSP-dependent expression of many competence-specific genes that share an unusual consensus sequence (TACGAATA) at their promoter regions. To test the hypothesis that this regulator acts as a transient alternative sigma factor, ComX was purified from an Escherichia coli overexpression strain and core RNA polymerase was purified from a comX-deficient S. pneumoniae strain. The reconstituted ComX-polymerase holoenzyme produced transcripts for the competence-specific genes ssbB, cinA, cglA, celA, and dalA and was inhibited by anti-ComX antibody, but not by anti-sigma(70) antibody. Western blotting using antibodies specific for ComX, sigma(70), and poly-His revealed a transient presence of ComX for a period of 15 to 20 min after CSP treatment, while RNA polymerase remained at a constant level and sigma(A) remained between 60 and 125% of its normal level. ComX reached a molar ratio to RNA polymerase of at least 1.5. We conclude that ComX is unstable and acts as a competence-specific sigma factor.
authors.affiliation: Laboratory for Molecular Biology, Department of Biological Sciences, University of Illinois at Chicago, 900 S. Ashland Avenue, Chicago, IL 60607, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Luo
authors.forename: Donald A
authors.initials: DA
authors.lastname: Morrison
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D013296:Streptococcus pneumoniae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014169:Transformation, Bacterial
chemical_list: D001426:Bacterial Proteins; C120829:ComX protein, Streptococcus; D012808:Sigma Factor; D014157:Transcription Factors; C423628:competence factor, Streptococcus; D012321:DNA-Directed RNA Polymerases