PLASMID RNA POLYMERASE-LIKE MITOCHONDRIAL SEQUENCES IN AGARICUS-BITORQUIS

A linear mitochondrial plasmid, pEM, found in certain isolates of the basidiomycete Agaricus bitorquis, potentially encodes virus-like DNA a nd RNA polymerases. Mitochondrial DNA from Agaricus bisporus that hybr idizes to an internal region of pEM contains a fragmented and potentia lly non-functional version of the carboxy terminal end of the plasmid RNA polymerase. In this study, we present the sequence of the correspo nding region of mitochondrial DNA from A. bitorquis. This sequence con tained the same region of the plasmid RNA polymerase gene as was repor ted for the mitochondrial DNA of A. bisporus, and the level of similar ity between the A. bisporus and A. bitorquis mitochondrial sequences w as much higher than the level of similarity between either mitochondri al sequence and the plasmid. We propose that this plasmid RNA polymera se-like sequence was present in the Agaricus mitochondrial genome befo re the divergence of A. bisporus and A. bitorquis, and thus is unlikel y to be a recent derivative of the plasmid pEM.