Studies on Components of RNA in Cardiac Muscle with Emphasis on the Rapidly Labeled 4 to 18 S Fraction

Abstract

Studies on RNA from cardiac muscle of rats were performed by labeling the RNA with 32 P, extracting it with phenol, and purifying it prior to fractionating and analyzing it on a sucrose density gradient. The major components of RNA found had sedimentation values of 28, 18, and 4 S. Early 32 P-labeled RNA ranged in size from 4 to > 45 S. Characterization of RNA from 4 to 18 S showed it to be more rapidly labeled and to have a higher turnover rate than 28 S RNA, to be located, at least in part, in the microsomes, and to have a base composition lower in guanine and cytosine content than 28 S RNA. Labeling of 4 to 18 S and 28 S RNA was equally inhibited by actinomycin. The possibility that 4 to 18 S RNA may represent a portion of messenger RNA in cardiac muscle is considered.