Abstract
The erf (essential recombination function) gene of Salmonella phage P22 was mapped by complementation between plasmids carrying parts of the P22 chromosome and superinfecting erf − phage. A segment of DNA shown by this method to contain the erf gene was sequenced. The sequence contains an open reading frame of 205 codons, starting with ATG, and followed by two tandem termination codons. Two erf − amber mutations result in changes in two different CAG codons in this sequence to TAG. The DNA sequence predicts an Erf protein monomer molecular weight of approximately 23,000. Two other conclusions emerge from the phage-plasmid complementation assay: Gene 17 of P22 is located between genes erf and c2; and phage λ encodes a function, possibly redβ, that can complement P22 erf −.
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