Mapping of additional restriction enzyme cleavage sites on bacteriophage MB78 enzyme.

A physical map of bacteriophage MB78 DNA indicating the cleavage sites for the enzyme Bg/II, ClaI, EcoRI, Pvull, Sa/! and SmaI comprising of a total of 34 cleavage sites have been constructed earlier. The cleavage sites for a few more restriction endonucleasesli ke ApaI, AvaI, Bg/!, Hindlll, KpnI and XhoI have now been mapped. A total of 72 cleavage sites on MB78 DNA are known by now. Relative positions of EcoRI I and J fragments which could not be decided earlier has now been determined.

Exclusion of temperature bacteriophage P22 by virulent bacteriophage MB78 of Salmonella typhimurium: competition for association with the replication complex.

MB78, a virulent bacteriophage of S. typhimurium does not allow other bacteriophages like P22 and 9NA to multiply in its presence. The exclusion of P22 by MB78 is found to be due to competition for common binding site(s) in the host cell membrane. As a result, P22 DNA fails to replicate in presence of MB78 DNA. Further, the sedimentation profile of P22 DNA in cells infected simultaneously with P22 and MB78 suggested fragmentation of P22 DNA. This may also contribute to the exclusion phenomenon.

Replication, maturation and physical mapping of bacteriophage MB78 genome.

Bacteriophage MB78 is a virulent phage of Salmonella typhimurium. The viral DNA is 42 kb in size and seems to be circularly permuted. We show that viral DNA replication is through concatemeric DNA formation which is subsequently converted into full length DNA through headful packaging. A restriction map of MB78 DNA for six restriction endonucleases e.g. BgIII, PvuII, ECORI, ClaI, SalI and SmaI has been constructed. The yield of certain fragments in less than molar amount is explained in terms of permutation and the headful mechanism of packaging. The packaging site (pac site) has been suggested.