title: An operator associated with autoregulation of the repressor gene in actinophage phiC31 is found in highly conserved copies in intergenic regions in the phage genome.
abstract: Previous reports have suggested that the repressor gene, c, of phiC31 is autoregulated and that likely operators are conserved inverted repeat sequences (CIRs1&2) located just upstream of the promoters, cp1 and cp2. Evidence is now presented that the CIRs 1&2 are indeed binding sites for one of the three inframe, N-terminally different protein isoforms of 42, 54 and 74 kDa produced by the c gene. A cp1-aphII fusion was repressed in a Streptomyces coelicolor A3(2) phiC31 lysogen and characterisation of an operator-constitutive (Oc) mutant showed a single mutation in CIR-1. CIR-1 containing fragments were retarded in electrophoresis gels by the 42 kDa repressor protein isoform and this retardation was inhibited by the addition of competing DNA fragments containing either CIR-1 or CIR-2. Using a combination of Southern blotting and analysis of available DNA sequence we also show that at least 18 copies of the CIRs are present throughout the phiC31 genome. Alignment of 9 CIR sequences showed that 8 contained a perfectly conserved 17 bp core whilst the exception had a single mismatch. The core includes a 16 bp inverted repeat (IR), and is usually part of a more extensive and less highly conserved palindrome. When superimposed on a previously derived transcription map of the early region, the CIRs lie in intergenic regions associated with transcription initiation and/or termination.
authors.affiliation: Robertson Institute of Biotechnology, University of Glasgow, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Ingham
authors.forename: C E
authors.initials: CE
authors.lastname: Owen
authors.forename: S E
authors.initials: SE
authors.lastname: Wilson
authors.forename: I S
authors.initials: IS
authors.lastname: Hunter
authors.forename: M C
authors.initials: MC
authors.lastname: Smith
mesh_terms: D001435:Bacteriophages / Q000235:genetics*; D001483:Base Sequence; D015139:Blotting, Southern; D017124:Conserved Sequence; D004279:DNA, Viral; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral; D007438:Introns; D008969:Molecular Sequence Data; D009154:Mutation; D009875:Operator Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000235:genetics*; D014764:Viral Proteins / Q000235:genetics*
chemical_list: D004279:DNA, Viral; D012097:Repressor Proteins; D014764:Viral Proteins