Studies of viable T4 bacteriophage containing cytosine-substituted DNA (T4dC phage). II. Cleavage of T4dC DNA by endonuclease SalI and bam HI.

Digestion of non-glucosylated and cytosine-substituted T4 phage (T4dC) DNA with SalI restriction endonuclease showed that the DNA had nine SalI-sensitive sites. There were eight SalI sites in DNA from a strain which had a deletion in the rII-denB-ndd region. The comparison of two digestion patterns indicated that one of the SalI-sensitive sites was present in the deleted region and that the SalI-F fragments (8.4 x 10(6) daltons) was located adjacent to the SalI-C or SalI-D fragments (15.5 x 10(6) daltons) on the T4 chromosome. The DNA gave no detectable cleavage product when digested with BamHI endonuclease alone, while, when digested successively with BamHI and SalI, the DNA yielded two new digestion products in place of one fragment formed by SalI alone. The BamHI-sensitive site was in the SalI-A fragment (25.2 x 10(6) daltons). The usefulness of this information for making cleavage maps of T4 phage chromosome is discussed.