[Comparative study of low molecular weight RNA in various taxonomic groups].

snRNAs of rat, mouse, hamster, chicken, frog, Drosophila and yeast were studied. Mammals are characterized by the highest content of snRNAs. Most evolutionary conservative are 8SII and 8SIII RNAs which were present in all organisms studied. On the contrary 4.5S RNA was found only in mammals and birds. These data accord with the notion that the eldest in the family of snRNAs are U3 RNA involved in pre-rRNA processing and 8S polysomal RNA, while U5-U6 RNAs are more recent evolutionary achievements. In the frog at different stages of development the relative amount and the number of fractions of snRNAs differ significantly. In embryonic and regenerating rat liver the differences are less pronounced. Extra fractions of snRNAs were found in virus transformed chick fibroblasts and in ascite hepatomas of rat.