| Abstract: | D3112 phage was shown to replicate via the process of coupled replication--transposition: the phage DNA is not excised from the chromosome after prophage induction and new phage copies insert into many different sites. The transposition is controlled by two D3112 early genes--A (mapped in the 1.5-3 kbp region) and B (3-4.5 kbp), and requires intact attL site (involvement of the phage right end attR not studied). D3112 is capable to transpose RP4 plasmid into the chromosome; both the D3112 and RP4 transpositions are rec-independent. The product of the early C gene which is not required for D3112 transposition has pleiotropic effect on the development of D3112 and is necessary for the process of D3112 DNA excision from the chromosome, for cell lysis as well as for mature phage production. We suggest that this gene is responsible for positive regulation of D3112 late genes expression, similar to the C gene of Mu phage or Q gene of lambda. Mutations in four D3112 late genes ts25, ts35, ts73 and ts110 do not affect transposition or excision processes. No detectable (less than 0.02 copies per cell) amount of linear or circular D3112 DNA is formed during the replication--transposition. Hence, in the course of replication and transposition processes D3112 genome has its ends permanently bound covalently to the chromosome. The excision of the D3112 DNA takes place at late stages. |
