title: Molecular cloning, sequence and expression of Aa-polB, a mitochondrial gene encoding a family B DNA polymerase from the edible basidiomycete Agrocybe aegerita.
abstract: An ORF of 1716 nucleotides, putatively encoding a DNA polymerase, was characterized in the mitochondrial genome of the edible basidiomycete Agrocybe aegerita. The complete gene, named Aa-polB, and its flanking regions were cloned and sequenced from three overlapping restriction fragments. Aa-polB is located between the SSU rDNA (5' region) and a gene for tRNA(Asn) (3' region), and is separated from these genes by two A + T-rich intergenic regions of 1048 (5' region) and 3864 (3' region) nucleotides, which lack repeated sequences of mitochondrial or plasmid origin. The deduced Aa-POLB protein shows extensive sequence similarity with the family B DNA polymerases encoded by genomes that rely on protein-primed replication (invertrons). The domains involved in the 3'-->5' exonuclease (Exo I to III) and polymerase (Pol I to Pol V) activities were localized on the basis of conserved sequence motifs. The alignment of the Aa-POLB protein (571 amino acids) with sequences of family B DNA polymerases from invertrons revealed that in Aa-POLB the N-terminal region preceding Exo I is short, suggesting a close relationship with the DNA polymerases of bacteriophages that have linear DNA. The Aa-polB gene was shown to be present in all wild strains examined, which were collected from a wide range of locations in Europe. As shown by RT-PCR, the Aa-polB gene is transcribed in the mitochondria, at a low but significant level. The likelihood of the coexistence of Aa-POLB and Pol gamma in the A. aegerita mitochondrion is discussed in the light of recent reports showing the conservation of the nucleus-encoded Pol gamma from yeast to human.
mesh_terms: D000363:Agaricales / Q000201:enzymology* / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics*; D005800:Genes, Fungal; D006801:Humans; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic