Developmental changes in the molecular weight of heterogeneous nuclear RNA

The size distribution of heterogeneous nuclear RNA (hnRNA) in the sea urchin embryo changes markedly during early development. Measurement of cleavage (4.5 h) to late gastrula (40 h) hnRNA by sedimentation in aqueous and denaturing solvent indicates that in the stages tested cleavage (4.5 h) hnRNA is smallest and rotating blastula (13 h) hnRNA is largest. The molecular weight of cleavage hnRNA is calculated to be about one-third that of rotating blastula hnRNA. Sedimentation of early embryo hnRNA in denaturing solvent to disaggregate complexes demonstrated mean S values lower than those obtained in aqueous solvent.