Transcriptional and translational analysis of the ccaR gene from Streptomyces clavuligerus.
CcaR is a positive-acting transcriptional regulator involved in cephamycin C and clavulanic acid biosynthesis in Streptomyces clavuligerus. Previous sequence analyses of the ccaR gene revealed two possible start codons, an ATG, and a GTG located in-frame 18 bp downstream of the ATG. To determine the true start codon, ccaR was expressed, either from the GTG or ATG codon, in Escherichia coli. A protein product was only obtained from the ATG construct. Similarly, ccaR constructs originating from ATG or GTG and designed for expression from a glycerol-regulated promoter in Streptomyces species were prepared and used to complement a S. clavuligerus ccaR mutant. Bioassays showed that only the ATG construct could complement the ccaR mutant to restore cephamycin C production, and Western analysis confirmed the presence of CcaR in the mutant complemented with the ATG construct only. To ensure that expression of ccaR from its native promoter also initiated at the ATG rather than GTG, a conservative point mutation was introduced into ccaR, converting the GTG to GTC. The GTC construct still fully complemented a ccaR mutant, confirming that ATG is the true start codon. Inspection of the region upstream of ccaR by S1 nuclease protection and primer extension analyses indicated the presence of two transcript start points that mapped to residues located 74 and 173 bp upstream of the ATG codon.
Wang
Liru
L
Department of Biological Sciences, University of Alberta, Edmonton, Canada T6G 2E9.
Tahlan
Kapil
K
Kaziuk
Tracy L
TL
Alexander
Dylan C
DC
Jensen
Susan E
SE
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002513:Cephamycins / Q000096:biosynthesis*; D019818:Clavulanic Acid / Q000096:biosynthesis*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D014176:Protein Biosynthesis; D013302:Streptomyces / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002513:Cephamycins; C112951:ClaR protein, Streptomyces clavuligerus; D014157:Transcription Factors; D019818:Clavulanic Acid; C024925:cephamycin C