title: The Streptococcus mutans IrvR repressor is a CI-like regulator that functions through autocleavage and Clp-dependent proteolysis.
abstract: Previous work has shown that irvR is required for the proper regulation of genetic competence and dextran-dependent aggregation due to its ability to repress the transcription regulator irvA. In this study, we determined the mechanism used to relieve the repression of irvA. We demonstrate that IrvR is a "LexA-like" protein with four conserved amino acid residues likely required for IrvR autocleavage activity. Furthermore, recombinant IrvR protein purified from Escherichia coli was competent to undergo autocleavage in vitro. Using several truncated IrvR constructs, we show that the amino acids adjacent to the autocleavage site are essential for relieving irvA repression and engaging the irvA-dependent regulatory pathway primarily through the ClpXP and ClpCP proteases. By extending the IrvR C terminus with an epitope derived from the autocleavage site, we were also able to create a constitutive Clp-dependent degradation of the full-length IrvR protein. This suggests that the derepression of irvA occurs through a two-step mechanism involving the initial autocleavage of IrvR and exposure of a proteolytic degradation sequence followed by Clp-dependent degradation of the IrvR DNA binding domain. Thus, irvA derepression is highly analogous to the genetic switch mechanism used to regulate lysogeny in bacteriophages.
authors.affiliation: Department of Oral Biology, College of Dentistry, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Niu
authors.forename: Toshinori
authors.initials: T
authors.lastname: Okinaga
authors.forename: Fengxia
authors.initials: F
authors.lastname: Qi
authors.forename: Justin
authors.initials: J
authors.lastname: Merritt
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018387:Codon, Initiator; D049071:Endopeptidase Clp / Q000235:genetics / Q000378:metabolism*; D000939:Epitopes; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008969:Molecular Sequence Data; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013295:Streptococcus mutans / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D018387:Codon, Initiator; D000939:Epitopes; D012097:Repressor Proteins; D049071:Endopeptidase Clp