Group I. and II. introns are present in Saccharomyces mitochondrial DNA (mtDNA) only within cox1, cob and rnl genes. A detailed analysis suggests cox1I3α insertion site in the position 242 in order to preserve conserved G-G-F-G-N motif. A number of introns also contain open reading frames (ORFs), with different homing endonuclease (HE) motifs, in phase with the upstream exon. The exceptions are cox1I5β and cobI1α, where alternative splicing takes place. Introns represent a class of mobile elements randomly distributed among the different species. There are a few remarkable exceptions like cox1I3β, which has not been found in S. cerevisiae but besides S. arboricolus in all other Saccharomyces species. Also, intron cox1I4α, was not identified in any other Saccharomyces but in S. cerevisiae. Very rare is the orphan cox1I4γ intron that occurs only in S. uvarum strains. Both, cox1I3β and cox1I4γ are considered as a main source of Dobzhansky–Muller nuclear incompatibilities that may result in the divergence of yeast species.

Keywords: mtDNA; introns; ORF; “homing endonucleases”; Saccharomyces

This work was supported by grants from the Slovak Grant Agency of Science (VEGA 1/0048/16).

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