Some Properties of RNA:Protein Complexes from the Nucleus of Eukaryotic Cells

The control of gene expression in prokaryotic organisms is generally thought to reside directly in the regulation of the synthesis of specific messenger RNA molecules, which immediately enter active polyribosomal structures. In eukaryotes, however, several components intervene between the transcription and translation of mRNA. There are RNA sequences in the nuclei of cells of higher organisms that are rapidly synthesized and destroyed without being transported to the cytoplasm (Harris, 1959; Houssais and Attardi, 1966; Shearer and McCarthy, 1967; Soeiro et al., 1968). Some rationale for these findings is provided by evidence that mRNA sequences are synthesized as part of giant heterogeneous nuclear RNA transcripts (HnRNA), which are subsequently cleaved to yield true mRNA molecules (Wagner and Roizman, 1969; Lindberg and Darnell, 1970; Williamson et al., 1973). During the processing of these nuclear RNA molecules, a polyadenylate sequence, poly(A), is apparently added at the 3′-OH end of most mRNA molecules (Edmonds...