Amber mutants of Salmonella-phage P22 in genes engaged in the establishment of lysogeny.

Abstract

Phage mutants were isolated with amber mutations in genes necessary for establishment of lysogeny. These mutants form turbid plaques on su+ strain 527R1 and clear plaques of different types on LT2. According to complementation tests, fourteen mutants fall in the c2 gene, four in the c3 gene but no amber mutants were found belonging to the c1 gene. Pulse labelling experiments to follow DNA synthesis after phage infection were done with the mutants classified by complementation tests. Furthermore the labelling experiments demonstrated that the nonleaky c3 amber mutants displayed the same DNA synthesis pattern as c1 missense mutants. Since these c3 amber mutants complement missense c1 mutants it is concluded that the c3 and c1 genes must act together for the first transient repression of DNA synthesis, i.e., seven minutes after infection. It is suggested that clear plaque forming c1 amber mutants cannot be isolated because of polarity leading to defectivity of lysogenic as well as of lytic functions.