Presence of a P1 bacteriophage sequence in transforming plasmids of Pleurotus ostreatus

Replicative plasmids pP01 and pP02, recovered from Pleurotus ostreatus transformants, contain an insert of bacteriophage origin. These plasmids have been amplified by the polymerase chain reaction (PCR) and have been shown to represent a low-grade component in the initial preparation of the vector pAN7-1. The pP01 and pP02 plasmids share an insert (P01A) of virtual identity with a SmaI-BamHI genomic fragment of P 1 bacteriophage and retain remnants of a polylinker at the 5' end of this fragment. Such an insert undoubtedly represents an in vitro-generated event and did not arise, as suggested previously, by recombination of pAN7-1 with the P. ostreatus genome. The P. ostreatus transformants, however, do select for the minority pP0 plasmid, apparently recognizing the P01A insert as a heterologous or surrogate replicon.