A DNA-polymerase-related reading frame ( pol-r) in the mtDNA of Secale cereale.

Mitochondrial (mt)DNA of Secale 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 the S1 plasmid of Zea mays; it contains the highly-conserved domains IIa to V of family B polymerases. The pol-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 of Z. mays and Triticum aestivum. The pol-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. [ABSTRACT FROM AUTHOR]