Analysis of the genetic complexity and abundance classes of messenger RNA in human liver and leukemic cells.

In an effort to determine the number of genes expressed as messenger RNA in disparate human tissues we have analyzed the genetic complexity of the polyribosome-associated poly(A)-containing RNA population obtained from liver and lymphoblastic leukemic cells. This was accomplished by measuring the kinetics of hybridization of mRNA to a complementary DNA probe synthesized by avian myeloblastosis virus reverse transcriptase in vitro. The results obtained from such an analysis revealed the presence of two major abundance classes of mRNA with a total genetic complexity of approximately 10,000 diverse mRNA species in both of these cell types. Diversity of mRNA species in these unrelated human cells was studied by heterologous hybridization reactions between the cDNA of one cell type and a vast excess of poly(A)-containing mRNA from another. These types of studies indicated that extensive homology (more than 80%) exists in the mRNA sequences of disparate human cell types and suggest that the vast majority of genetic information expressed as mRNA is required for the maintenance of cellular functions common to functionally different human tissues.