Studies on rapidly labelled ribonucleic acid in HeLa cells

A study of the sedimentation pattern in sucrose gradients of rapifly-labelled RNA (5-30 min labelling with [14C]adenine) was done on whole extracts of HeLa cells. Two regions of radioactivity have been found: a lighter region sedimenting in the range of 4 to 20-S particles and a heavier heterogeneous region sedimenting from about 30 S to the bottom of the gradients even when 30 % sucrose was used. The nature of the various types of RNA's likely to sediment in these regions is discussed. The heavier heterogeneous region contained very small amounts of DNA, but no definite evidence for the existence of DNA-RNA hybrids was obtained. On the other hand, the heavy heterogeneous region is active in amino acid incorporation and consisted of a variety of polysomes; their characterization by electron microscopy is described in a further paper. These polysomes, after a short labelling period, consist of unlabelled 74-S ribosomes to which is attached rapidly-labelled RNA; it was shown that it takes roughly 5 min for [14C]adenine to become integrated into RNA sedimenting with the polysomes. Comparison of autoradiographic and sedimentation analysis shows that a large proportion of the polysomes might be formed in the cell nucleus. © 1964.SCOPUS: ar.j