High molecular weight nonribosomal-type nuclear RNA and cytoplasmic messenger RNA in HeLa cells.

As reported elsewhere,[1] the study of RNA synthesis in vitro in immature duck erythrocytes has revealed the occurrence in the nucleus of fast turning-over RNA of high molecular weight (from 2 X 10^6 to 10^7, or possibly more) and with base composition different from that of ribosomal RNA, and characterized by a high U and relatively low GC content. No relationship of precursor-to-product type -- or, at any rate, not a simple one-appears to exist between this RNA and the messenger RNA fraction associated with cytoplasmic polysomes. In this paper, evidence is presented indicating that this class of nuclear RNA molecules is not exclusive of immature erythrocytes, or in general of nondividing cells undergoing differentiation, but occurs also in exponentially growing cells.