[Separation of rat thymocyte populations in a ficoll-paque gradient. IV. The genetic complexity of the cellular RNA of thymocyte subfractions].

The sequence complexity of the total cellular RNA was measured by RNA-driven hybridization to 125I-single copy DNA (sc-DNA). In the high density subfraction of thymocytes 4.5% of sc-DNA was saturated with cellular RNA. The sc-DNA probe was recovered from the DNA--RNA hybrids and rehybridized with homologous RNA and heterologous RNA from the cells with low density and middle density. Heterologous hybridization reactions with recycling sc-DNA probes revealed that 5.5% RNA sequences were specific of the cells from the high density subfraction and absent in both low and middle density subfractions. This is equivalent to expression of approximately 1100 additional structural genes in the high density subfraction of thymocytes.