Preliminary Study on the Metabolic Characteristics of Supernatant 5SRNA of the Rat Liver

The 5' - and 3' -terminal sequences of the rat liver supernatant 5SRNA were shown to be the same as the corresponding sequences of ribosomal 5SRNA. The time course of the specific activity of the supernatant 5SRNA in the livers of rats receiving an intraperitoneal injection of [^3H] orotic acid showed that there was no lag in the labeling of this RNA, and that the specific activity increased up to 3 h and then decreased. The specific activity of ribosomal 5SRNA increased gradually after a lag of 90 min. The specific activity of supernatant 5SRNA was markedly higher than that of ribosomal 5SRNA at each time of labeling. These findings indicate a high metabolic rate for supernatant 5SRNA of rat liver