Project description:Ribosomes are ribonucleoprotein complexes highly conserved across all domains of life. The size differences of ribosomal RNAs (rRNAs) can be mainly attributed to variable regions termed expansion segments (ESs) protruding out from the ribosomal surface. Although the ESs were found to be involved in a range of processes including ribosome biogenesis and maturation, translation, and co-translational protein modification, their roles remain largely elusive. Here, we analyze the rRNAs of the yeasts from the Magnusiomyces/Saprochaete clade belonging to the basal lineages of the subphylum Saccharomycotina. We find that these yeasts lack more than 400 and 150 nt from the 25S and 18S rRNAs, respectively, when compared with “canonical” counterparts. With a few exceptions, the missing regions map to ESs thus representing a shift toward minimal rRNA structure raising a question about their roles. On the other hand, we show that the ribosomal protein inventories remained unaffected. We also show that the shortening of ESs is not limited to the species of the Magnusiomyces/Saprochaete clade as the rRNA reduction happened independently in several other lineages of the subphylum Saccharomycotina.
