Ribonucleic Acid Biosynthesis in Human Leukocytes: The Fate of Rapidly Labeled RNA in Normal and Abnormal Leukocytes

Abstract

Abstract Ribonucleic acid (RNA) was isolated from a variety of human leukocyte populations exposed to tritiated uridine in vitro. Several species of RNA were extractable from leukocytes in a phenol-water system. With mild conditions of extraction a pH 7.6 fraction was obtained, which contained 60 to 75 per cent of total cellular RNA. After removal of this RNA component reextraction at elevated temperature and pH yielded a pH 9 fraction which contained 25 to 40 per cent of total cellular RNA. The pH 7.6 fraction contained 28 and 18 S ribosomal RNA and 4 S RNA. The pH 9 RNA fraction was heterogeneously distributed in a sucrose density gradient. The 28 and 18 S components were slowly labeled by H3-uridine and were relatively stable. The 4 S component was rapidly labeled and was unstable. The pH 9 RNA fraction contained most of the rapidly labeled RNA, which was either of high molecular weight or heterogeneous as to molecular size. The pattern of incorporation of H3-uridine into the various components of RNA was similar in normal and neoplastic granulocytes and lymphocytes. Rapidly labeled leukocyte RNA had the following characteristics: (1) its synthesis was actinomycin sensitive; (2) it was unstable, having a half-life in the range of 16 to 225 minutes; and (3) it was in part a precursor of ribosomal RNA. The sensitivity of granulocyte protein synthesis to inhibition of RNA synthesis suggests that granulocytes have both stable and unstable templates.