Identification of human DNA sequences complementary to chromosomal RNA with an improved RNA/DNA gradient hybridization technique

Native DNA components in the human genome were identified with an improved RNA gradient hybridization technique. ³H-Labelled complementary RNA transcribed from total human DNA was hybridized to homologous DNA which had been mildly sheared to generate single-stranded ends. Unhybridized RNA was eliminated from the reaction mixture by column chromatography before the hybrids were subjected to CsCl gradient centrifugation. Nine radioactive peaks representing RNA hybrids were reproducibly found at buoyant densities of 1.687, 1.693, 1.696, 1.699, 1.702, 1.705, 1.708, 1.711 and 1.715 g/cm³. The technique was also utilized to hybridize ¹²⁵I-labelled human chromosomal RNA to DNA. Three distinct radioactive peaks were found at the heavy buoyant densities of 1.702, 1.705, and 1.708 g/cm³, suggesting a differential enrichment of DNA components with sequences complementary to chromosomal RNA.