SUPERINFECTION EXCLUSION (SIEB) GENES OF BACTERIOPHAGES P22 AND LAMBDA

The superinfection exclusion gene (sieB) of Salmonella phage P22 was m apped with phage deletion mutants. The DNA sequence in the region was reexamined in order to find an open reading frame consistent with the deletion mapping. Several discrepancies with the previously published sequence were discovered. The revised sequence revealed a single open reading frame of 242 codons with six likely translation initiation cod ons. On the basis of deletion and amber mutant phenotypes, the second of these six sites was inferred to be the translation initiation site of the sieB gene. The sieB gene encodes a polypeptide with 192 amino a cid residues with a calculated molecular weight of 22,442, which is in reasonable agreement with that estimated from polyacrylamide gels. Th e transcription start site of sieB was identified by the use of an RNa se protection assay. The sieB promoter thus identified was inactivated by a 2-base substitution in its -10 hexamer. The sieB gene of colipha ge lambda was also identified. The promoter for lambda sieB was identi fied by homology to that of P22 sieB.