Chicken ribosomal DNA: Gene frequency and purification by R-loop hybridization

Abstract

The genes for ribosomal RNA of chicken are present in about 200--240 copies per haploid genome. The ribosomal genes were separated from the bulk of DNA by different methods. In CsCl-actinomycin D gradients the GC-rich ribosomal DNA is shifted to the lower density side of the bulk of DNA. After hybridization with iodinated ribosomal RNA under conditions where R-loops are formed ribosomal DNA has an increased density. The R-loops can be separated from the bulk of DNA in Cs2-SO4 gradients.

Dna Damage and Repair in Human Cells Exposed to Sunlight

“…Weight average mol. wt (M,) were calculated using the relationship given by Lehmann (1972), without correction for the reduction in sedimentation rate at high speed.…”

“…Thymidine incorporation in the presence of hydroxyurea was used as an independent method, and to facilitate dose response studies. Hydroxyurea inhibits the joining of DNA strands (Lehmann, 1972;Collins er al., 1977) but apparently does Figure 6. DNA repair synthesis in PGP fibroblasts as determined by thymidine incorporation in the presence of hydroxyurea.…”

Pyrimidine Dimer Sites Associated With the Daughter Dna Strands in Uv‐irradiated Human Fibroblasts

“…Whether these are caused by a slower rate of elongation between lesions (unlikely as shown by Povirk and Painter, 1976) or a delay at lesions followed either by gap formation and sealing (e.g. Lehmann, 1972) or by continuous synthesis past the lesions (e.g. see Higgins et a[., 1976;Fujiwara and Tatsumi, 1976; is not relevant for our calculations.…”

“…Since some of the DSDS must be attached DSDS the frequency of exchanged DSDS must be less than 10% of the frequency of dimer sites in parental DNA, and would not therefore have been detected in density labelling experiments (Lehmann, 1972;Painter, 1974;Fujiwara and Tatsumi, 1977). Very low levels of UVinduced recombinant-like molecules have been detected in Chinese hamster cells (Rommelaere and Miller-Faures, 1975), and some kind of recombinational exchanges are known to be produced during replication of DNA in UV-irradiated cells since UV produces an increased number of sister-chromatid exchanges in a variety of mammalian cells (Kato, 1973(Kato, , 1974Wolff et al, 1974;De Weerd-Kastelein et al, 1977).…”

“…In contrast to the bacterial situation, attempts to detect exchanges of large tracts of DNA between parental and daughter DNA strands after UV-irradiation have been unsuccessful (Lehmann, 1972;Fujiwara and Kondo, 1974;Painter, 1974). There have, however, been several recent reports of the detection of pyrimidine dimer sites associated with newly-synthesized DNA in UV-irradiated mammalian cells (Buhl and Regan, 1973;Hanawalt, 1975, 1976;Waters and Regan, 1976;Waldstein and Setlow, 1976;Fujiwara and Tatsumi, 1977).…”