The mosaic organization of the mitochondrial introns of Saccharomyces cerevisiae: features and evolutionary origins.
The introns of three genes (oxi3, cob and 21S) from the mitochondrial (mt) genome of Saccharomyces cerevisiae contain closed reading frames (CRFs). In the present work, we have analyzed these sequences in their oligodeoxyribonucleotide (oligo; isostich) patterns. We have shown that the relative amounts of di- to hexanucleotides, when compared to random sequences having the same sizes and compositions, exhibit the same deviations as the intergenic noncoding sequences of the mt genome (except for the CRFs from 21S intron). In contrast, intronic open reading frames (ORFs) showed oligo patterns which were generally quite distinct from those of CRFs, although some similarities could be detected in some cases (especially for aI5 alpha). The mt introns of yeast, therefore, are endowed with a mosaic structure, in which CRFs derive from mt intergenic sequences, whereas ORFs have a different origin (indicated as exogenous by other evidences) yet show, in some cases, the effects of 'sequence assimilation' with CRFs.
de Zamaroczy
M
M
Laboratoire de Génétique Moléculaire, Institut Jacques Monod, Paris, France.
Bernardi
G
G
D001482:Base Composition; D005075:Biological Evolution; D005800:Genes, Fungal; D007438:Introns; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D009030:Mosaicism; D016366:Open Reading Frames; D012441:Saccharomyces cerevisiae / Q000235:genetics*