Conservation of meiosis-specific nuclear proteins in eukaryotes: a comparative approach

Abstract

Hundreds of proteins function in cell nuclei during meiosis in plants, fungi and animals, a quarter of them being meiosis specific. Enzymes of DNA recombination are considered the most conserved; in contrast, structural proteins of meiotic chromosomes often have no orthologs outside their taxa. This especially concerns proteins that form synaptonemal complexes (SCs). Estimations of the similarity or phylogenetic relations between proteins of the same function in different organisms differ between researchers. We aimed to apply a simple quantitative method of stepwise and pairwise comparisons of amino acid sequences to evaluate the degree of similarity within groups of meiosis-specific proteins in different phylogenetic lineages of eukaryotes. We established that the recombination proteins RAD51, DMC1 and MLH1 are more conserved than the structural proteins of meiotic chromosomes. However, their functional domains are only slightly more conserved than the whole molecules in RAD51, DMC1 and MLH1 or are not conserved at all in meiotic endonuclease SPO11. In general, the proteins that provide for precise DNA strand exchange (RAD51 and DMC1) are more conserved than other recombination proteins (MLH1 and SPO11). Concerning variable structural proteins of meiotic chromosomes, cohesins and some SC proteins, we found the similarity of their functional domains to be two to five times higher than that of the whole molecules, which probably reflects the function of these domains to bind DNA. Our data are consistent with the suggestion that there is high selection pressure on the sequence of DNA strand exchange proteins RAD51 and DMC1 and less selective pressure on resolvase MLH1. A more detailed investigation of variability in SPO11 endonuclease is needed.