Duplication of a Truncated Paralog of the Family B DNA Polymerase Gene Aa-polB in the Agrocybe aegerita Mitochondrial Genome

Abstract

ABSTRACT The Agrocybe aegerita mitochondrial genome contains a truncated family B DNA polymerase gene ( Aa-polB P1 ) whose nucleotide sequence is 86% identical to 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 P1 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 mitochondrial tRNA locus. Two naturally occurring alleles of Aa-polB P1 carry one or two copies of the disrupted sequence. In strains with two copies of Aa-polB P1 , these copies are inverted relative to one another and separated by a short sequence carrying the tRNA Met gene. Both A. aegerita mitochondrial family B DNA polymerases were found to be related to other family B DNA polymerases (36 to 53% amino acid similarity), including the three enzymes of the archaebacterium Sulfolobus solfataricus . If mitochondria originated from a fusion between a Clostridium -like eubacterium and a Sulfolobus -like archaebacterium, then the A. aegerita family B DNA polymerase genes could be remnants of the archaebacterial genes.