Alignment of a restriction map with the genetic map of bacteriophage T4

A restriction map of the bacteriophage T4 genome was aligned with the T4 genetic map. Included were the cleavage sites for BamHI, BglII, KpnI, PvuI, SalI, and XbaI. The alignment utilized the fact that the T4 genetic map had been oriented previously with respect to a T2/T4 heteroduplex map. DNA fragments from a BglII digestion of cytosine-containing DNA from a T4 dCTPase- denA denB(rIIH23B) alc mutant were hybridized with full-length chromosomal strands of bacteriophage T2, and the heteroduplexes were examined by electron microscopy. From their lengths and patterns of substitution and deletion loops, the heteroduplexes formed with 6 of the 13 BglII fragments could be unambiguously identified and positioned on the T2/T4 heteroduplex map. The ends of the T4 DNA strands in the heteroduplexes directly identified the location of 10 BglII cleavage sites. The remaining three BglII cleavage sites could be assigned to the T2/T4 heteroduplex map based on their relative locations on the restriction map. It was also possible to identify the source of the DNA strands (i.e., T2 or T4) in four previously unassigned deletion loops on the T2/T4 heteroduplex. Among the BglII fragments identified in heteroduplexes was the fragment containing the rIIH23B deletion; this deletion was used as the primary point of reference for alignment of the T4 restriction map with the T2/T4 heteroduplex map and, hence, with the T4 genetic map.