Analysis of the C-value paradox by molecular hybridization.

Poly(A)-containing RNA was isolated from ovaries of Xenopus laevis laevis and Triturus cristatus carnifex and used as a template for the synthesis of radioactive complementary DNA with RNA-dependent DNA polymerase. When annealed with an excess of homologous DNA, the complementary DNA is rendered double-stranded with kinetics that suggest that the coding sequences are single-copy in both these organisms. In Triturus, these sequences are distinct from the majority of the genome, which consists of repeated sequences, and distinct from the ribosomal cistrons, which are present in proportion to the increase in C-value relative to the Xenopus genome. Moreover, the number of different poly(A)-containing molecules in the ovary (sequence complexity) is the same in Xenopus and in Triturus.