Suppressor-sensitive mutants of coliphage phi80.

About fifty suppressor sensitive (sus) mutants of phage phi80 were isolated after hydroxylamine treatment, and these were classified into fourteen cistrons. In vitro and in vivo complementation experiments revealed that at least five cistrons were concerned with head formation and that at least six cistrons were concerned with tail formation in phi80. Some presumed "early" mutants were also found. Defective lysogens were isolated from a phi80-lysogenic nonpermissive strain using the colicin plate method (Gratia, 1966). In these strains deletions which affected the colicin B receptor gene extended for varying distances into prophage phi80. Marker rescue experiments were carried out with these deletion lysogens by infecting various sus mutants, and the gene order in prophage phi80 was determined. Clustering of all head genes and also of tail genes, as in phage lambda, were demonstrated by the results of the prophage deletion mapping as well as the two-factor crosses performed among the sus mutants. Moreover, the gross gene arrangement of phi80 was also similar to that of phage lambda: namely, the cluster of head genes was found to be located at one end of the vegetative map of phi80, being followed by that of tail genes, and presumed "early" genes are located at the other end of the map.