Analysis of a linear plasmid isolated from the pathogenic fungus Ceratocystis fimbriata Ell. & Halst.

Summary A linear DNA plasmid, designated pCF637, was isolated from the fungus Ceratocystis fimbriata Ell. & Halst. strain CF637. It has an apparent molecular weight of 5.3 × 10⁶ daltons (8.2 kb). A restriction pattern of pCF637 using the enzymes AvaI, EcoRV and HpaII, was done. That pCF637 was sensitive to exonuclease III, but resistant to -exonuclease, suggest that there might be a protein associated with the 5 termini. The blocking action of the protein on -exonuclease was not eliminated by treatment with either pronase or proteinase K. The plasmid was also checked for homology with pFQ501, a linear plasmid found in strain CF560 of Ceratocystis fimbriata. By Southern hybridization under moderate stringency conditions, no homology was detected. The approximate copy number of the plasmid was estimated to be about 20–30 copies per cell by scanning, with a laser densitometer, a gel electrophoretic Polaroid^TM negative. No function is known for these plasmids.