Following a 1-h [3H]uridine pulse of cells of a human colon carcinoma line, 15% of the radioactivity in heterogeneous nuclear RNA associated with both chromatin and nuclear ribonucleoprotein was not digested to acid soluble fragments during a 2-h incubation with staphylococcal nuclease (EC 18.104.22.168). These [3H]uridine-labeled oligonucleotides were approximately 26 nucleotides in length. An RNA containing structure which sedimented no faster than 2 S could be isolated from the digests. Major and minor peptide species, of molecular weights 40 000 and 66 000, respectively, were associated with this structure isolated from either chromatin or nuclear ribonucleoprotein. The results demonstrate that some protein of nuclear ribonucleoprotein is complexed with the transcript while it is still associated with chromatin.
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