Abstract
Studies over the past decade have shown a significant role of synonymous mutations in posttranscriptional regulation of gene expression, which is particularly associated with messenger RNA (mRNA) secondary structure alterations. Most studies focused on prokaryote genomes and the nuclear genomes of eukaryotes while little is known about the regulation of mitochondrial DNA (mtDNA) gene expression. This paper reveals signs of selection in synonymous sites of the mitochondrial cytochrome b gene (Cytb) of Baikal oilfish or golomyankas (Comephoridae) directed towards altering the secondary structure of the mRNA and probably altering the character of mtDNA gene expression. Our findings are based on comparisons of intraspecific genetic variation patterns of small golomyanka (Comephorus dybowski) and two genetic groups of big golomyanka (Comephorus dybowskii). Two approaches were used: (i) analysis of the distribution of synonymous mutations between weak-AT (W) and strong-GC (S) nucleotides within species and groups in accordance with mutation directions from central to peripheral haplotypes and (ii) approaches based on the predicted mRNA secondary structure.