A DNA-polymerase-related reading frame (pol-r) in the mtDNA ofSecale cereale

Abstract

Mitochondrial (mt)DNA ofSecale cereale contains an open reading frame (pol-r), the potential translation product of which shows significant homology to the type-B DNA polymerase encoded by theS1 plasmid ofZea mays; it contains the highly-conserved domains IIa to V of family B polymerases. Thepol-r ORF is transcribed, as proven by RT-PCR, but the transcript is not edited. Upstream of the putative start codon a potential promoter motif was detected, fitting well into the postulated consensus sequence of the transcription initiation regions ofZ. mays andTriticum aestivum. Thepol-r ORF occurs in mtDNA of the fertile rye variety “Halo” and the cytoplasmic male-sterile (CMS) line “Pampa”. Both ORFs are almost identical, apart from the 3′ terminus;pol-r from Halo can code for 289 amino acids,pol-r from Pampa for 312 amino acids. Based on codon usage and the lack of editing,pol-r is considered to be a “young” gene, probably introduced in the mtDNA of rye by recombination with an mt plasmid.