FIG. 3.

Functional test for identification of the terminase genes. Outline of detecting cos cleavage by Southern hybridization (A). The probe overlapped the cos site, and hybridized to three fragments, derived from the EcoRI-digested concatemeric phage DNA. The uncut cos fragment (a) was indicated by the intact 92EcoRI-14EcoRI fragment (8,317 bp), while cos cleavage resulted in two more fragments, the right end-fragment (b) (92EcoRI-cos_right; 4,915 bp) and left end-fragment (c) (cos_left-14EcoRI; 3,402 bp). Detection of cos cleavage following prophage induction of lysogenic R. meliloti 41 containing phage 16-3cti3Km-154 and 16-3cti3Km-525 (B) and 16-3cti3Km-171 and 16-3cti3Km-249 (C). Lane 16-3 contained purified phage DNA digested with EcoRI, and samples from 16-3cti3 induction served as a positive control. Elapsed time following prophage induction is indicated in minutes. (Note that fragments a and b, derived from the Km mutant phage DNAs, migrated slower than the appropriate control fragments, since they contained the 1.2-kb Km cassette.)