SEQUENCE OF THE ESSENTIAL EARLY REGION OF PHI-C31, A TEMPERATE PHAGE OF STREPTOMYCES SPP WITH UNUSUAL FEATURES IN ITS LYTIC DEVELOPMENT

The temperate phage phi C31 is the most studied bacteriophage infectin g Streptomyces spp., and has been used to develop an extensive and wid ely used series of cloning vectors. The sequence of 10 kb of phi C31 D NA containing most or all of the essential early genes was determined. Among the ORFs, 14 (perhaps 15) appear to be protein-coding, and thes e have been designated ORF1 to ORF14 and ORFX. Previously mapped trans cripts appear to initiate upstream from ORFs 1, 8, 11 and 12, and with in ORF3 and ORF12, in each case close to one example of the unusual (' 21-mer') sequences that appear to serve as a recognition site for RNA polymerase early in the phi C31 lytic cycle [Ingham et al., Mol. Micro biol. 9 (1993) 1267-1274]. Further copies of the 21-mer are upstream f rom ORF2 and ORF13. There are four recognisable examples of a conserve d inverted repeat sequence motif (CIR) thought to bind phi C31 repress or [Smith and Owen, Mol. Microbiol. 5 (1991) 2833-2844]. Only one CIR is closely associated with a 21-mer sequence, though three are located between known transcription units. Of all 14 ORFs, only one (ORF11) w ould encode a protein unmistakably resembling other known proteins; it s product appears to be a DNA polymerase. Strikingly, two codons, TTA (Leu) and AGG (Arg), are absent from the 14 ORFs.