The old (overcoming lysogenization defect) gene product of bacteriophage P2 kills Escherichia coli recB and recC mutants and interferes with phage lambda growth [Sironi et al., Virology 46 (1971) 387-396; Lindahl et al., Proc. Natl. Acad. Sci. USA 66 (1970) 587-594]. Specialized transducing lambda phages, which lack the recombination region, can be selected by plating lambda stocks on E. coli that carry the old gene on a prophage or plasmid [Finkel et al., Gene 46 (1986) 65-69]. Deletion and sequence analyses indicate that the old-encoded protein has an Mr of 65,373 and that its transcription is leftward. Primer extension analyses locate the transcription start point near the right end of the virion DNA. A bacterial mutant, named pin3 and able to suppress the effects of the old gene, has been isolated [Ghisotti et al., J. Virol. 48 (1983) 616-626]. In a pin3 mutant strain, carrying the old gene on a prophage or plasmid, the amount of old transcript is greatly reduced. The effect of the pin3 mutation is abolished by the wild-type allele of argU, an arginine tRNA that reads the rare Arg codons AGA and AGG, which are used for eight of the 14 Arg codons in the old gene. Thus the pin3 allele probably stalls translation of the old mRNA, causing this mRNA to be degraded. Isoelectric focusing and electrophoretic analysis identify the old gene product as a basic protein of approx. 65 kDa.