Evidence for en bloc incorporation of exogenous oligonucleotides into HeLa cell RNA

3H uridine and 3H guanosine labeled oligonucleotides were separately produced by degradation of high molecular weight RNA by endogenous intracellular ribonucleases of HeLa cells. After incubation of this low molecular weight RNA with HeLa cells under conditions limiting labeled mononucleotide incorporation, significant label was found in high molecular weight 18s RNA, but not in 28s RNA. The label in the 18s RNA was alkali labile and remained with the 18s RNA peak under denaturation conditions. Actinomycin in the incubation mixture prevented the appearance of label in the 18s RNA. These results raise the possibility that exogenous oligonucleotide segments can be incorporated en bloc into RNA.