[Properties of different classes of low molecular weight RNAs]

Low molecular weight (LMW) RNAs from early fish embryos were characterized by investigating their migration in polyacrylamide gels, solubility in 1.5 M NaCl, in vivo methylation by the methionine methyl group, metabolic stability, and effects of low doses of alpha-amanitin on their syntheses. At blastula stage, the mature tRNA and 4.3--4.8 S metabolically unstable molecules described as precursors of tRNA in pulse-chase experiments were found. The syntheses of stable methylated LMW RNAs, different from tRNA, were also shown. The sizes of these molecules, determined by their migration in polyacrylamide gels, were 5.3S; 5.8S; 6.3S and 6.9S These RNAs resemble the nuclear LMW RNAs, discovered in different animal cells, in infertilized eggs and developing embryos of sea urchin among them. The data obtained allow one to suppose an existance of a maturation stage during formation of these RNAs. The synthesis of a certain fraction of LMW RNAs (4.9S) was sensible to low doses of alpha-amanitin and therefore involved RNA-polymerase II.