Mapping of the h and hh* host-range mutations in phage λ by two-point crosses with reference J- point mutations, and with λgal 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* × Jt-, 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 λ. 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 λ 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 λh+ 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 λ and 434.
Bibliographical noteFunding Information:
We are grateful to Maxime Schwartz and Maurice Hofnung, Pasteur Institute, Paris, for providing h and hh* phage strains and for communicating the results of their experiments prior to publication. This work has been supported by grants from the Medical Research Council of Canada.