Small nuclear rnas in cellular growth and differentiation. I: Metabolic alterations seen in friend erythroleukemic cells

Electrophoretic analysis of near steady‐state labeled nuclear RNA obtained from Friend virus‐transformed murine erythroleukemic cells reveals the presence of at least 15 small nuclear RNAs (snRNAs) distinct from ribosomal 5.8S or 5S. Identical qualitative distributions were obtained from logarithmically growing, stationary‐phase, and dimethyl sulfoxide‐induced, terminally differentiated cultures, indicating the constitutive synthesis of all snRNAs regardless of the proliferative or differentiated state of the cells. However, several quantitative differences in nuclear snRNA levels were observed. Progression from rapidly growing to stationary‐phase cultures was accompanied by the marked reduction in accumulation of all snRNAs except the 4.5S snRNAs. Particularly striking were the decreases in levels of U3 and the U1 group, snRNAs that are relatively abundant. Similar reductions were noted when cells were induced to differentiate, except that decreases in the levels of U2 and 4.5S were more dramatic than those seen for cells entering stationary‐phase. The data thus demonstrate that snRNA levels may be regulated both in association with changes in proliferative capacity of cells and with changes in gene expression that occur during terminal differentiation.