Duplication of a truncated paralog of the family B DNA polymerase gene Aa-polB in the Agrocybe aegerita mitochondrial genome

The Agrocybe aegerita mitochondrial genome contains a truncated family B DN A polymerase gene (Aa-polB P1) whose nucleotide sequence is 86% identical t o the previously described and potentially functional-Aa-polB gene. A tRNA( Met) gene occurs at the 3' end of the Aa-polB P1 gene. The Aa-polB PI gene could result from reverse transcription of an Aa-polB mRNA primed by a tRNA (Met) followed by the integration of the cDNA after recombination at the mi tochondrial tRNA locus. Two naturally occurring alleles of Aa-polB P1 carry one or two copies of the disrupted sequence. In strains,vith two copies of Aa-polB PI, these copies are inverted relative to one another and separate d by a short sequence carrying the tRNA(Met) gene. Both A, aegerita mitocho ndrial family B DNA polymerases were found to be related to other family B DNA polymerases (36 to 53% amino acid similarity), including the three enzy mes of the archaebacterium Sulfolobus solfataricus. If mitochondria origina ted from a fusion between a Clostridium like eubacterium and a Sulfolobus-l ike archaebacterium, then the A. aegerita family B DNA polymerase genes cou ld be remnants of the archaebacterial genes.