Comparative DNA-RNA hybridization in differentiated cells

Some hydrodynamic and spectral properties, as well as the capability to form RNA-DNA hybrids, have been measured for avian DNA. The DNA sources were red cells from adult chickens and from embryos at particular stages of differentiation, and selected adult chicken tissues. Sedimentation coefficients corresponded to an average molecular weight of 15 × 10 6 for red cell DNA, and to 11.4 × 10 6 for DNA from adult tissues. Determinations of T m for these DNA samples showed values ranging from 85.0 to 85.6 °C with an average of 85.3 ± 0.3 °C, corresponding to a G + C content of 39.0%. The hybridization conditions used permitted specific interaction between chicken DNA and reticulocyte 10 s RNA. Escherichia coli, Bacillus cereus and crab DNA tested in this sytem produced less than 15% hybridization on a scale placing chicken DNA at 100%. Competition experiments with total yeast RNA or chicken ribosomal RNA, added at concentrations as high as ten times that of the 10 s RNA, did not diminish the percentage of 10 s RNA hybridized. On the other hand, cold 10 s RNA showed a competitive effect under the same experimental conditions. In experiments designed to test whether a highly differentiated organism keeps the same genomal information in various tissues, no differences in capacity to hybridize with “Hb”-messenger RNA were detected. The same level of hybridization of reticulocyte 10 s RNA was detected with DNA from red cells at different stages of differentiation and with DNA from tissues of markedly different embryonic origin. It was not possible to reach saturation concentrations of 10 s RNA for the chicken DNA. When 30 times more RNA than DNA was present, approximately 2.5% hybridization was obtained. The meaning of this high percentage of hybridization is discussed.