The multisite character of host-range mutations in bacteriophage lambda.

Mapping of the h and hh * host-range mutations in phage lambda by two-point crosses with reference J- point mutations, and with lambdagal deleted for part of J, locates these mutations in the promoter-distal portion of the J cistron. Analysis of phenotypic h+ recombinants, formed in crosses of the type h or hh* x J-, or h+ revertants of h, hh* , and Jdef mutants, indicates that such phenotypic h+ particles often retain cryptic h determinants. Similar determinants are also present in some common laboratory strains of lambda. These h+ recombinants and revertants carry a variety of different h markers, since recombination analysis allows several classes of particles carrying cryptic h markers to be distinguished. These genetic data suggest that the extended host-range phenotype in lambda is due to multiple rather than single, mutations in the distal region of gene J, although the number of sites involved and their arrangement remain uncertain. The genetic location of the h and hh * mutations is confirmed at the physical level by comparing the tryptic peptide maps of the J proteins purified from lysates of cells infected with different h+, h, hh*, Jam, and J434 phage and from purified lambdah+ virions. Examination of these peptide maps shows there are several methionine-containing peptides altered in the h and hh * maps. Some of these altered peptides are derived from the C-terminal 5-10% of the J polypeptide in the region of nonhomology between lambda and 434.