PRESENCE OF A BACTERIOPHAGE-P1 SEQUENCE IN TRANSFORMING PLASMIDS OF PLEUROTUS-OSTREATUS

Replicative plasmids pP01 and pP02, recovered from Pleurotus ostreatus transformants, contain an insert of bacteriophage origin. These plasm ids have been amplified by the polymerase chain reaction (PCR) and hav e been shown to represent a low-grade component in the initial prepara tion of the vector pAN7-1. The pP01 and pP02 plas mids share an insert (P01A) of virtual identity with a SmaI-BamHI genomic fragment of P1 b acteriophage and retain remnants of a polylinker at the 5' end of this fragment. S uch an insert undoubtedly represents an in vitro-generate d event and did not arise, as suggested previously, by recombination o f pAN7-1 with the P. ostreatus genome. The P. ostreatus transformants, however, do select for the minority pP0 plasmid, apparently recognizi ng the P01A insert as a heterologous or surrogate replicon.