Transcription of the nonrepeated fraction of "accessible" DNA in rat liver chromatin.

Abstract

The relationship between structure and function in eukaryotic chromatin has been studied in rat liver cells. To elucidate the functional significance of "accessible" DNA, the transcription of this DNA (prepared by titration of liver chromatin with poly-D-lysine) has been examined by RNA-DNA hybridization. The maximum extent to which nuclear RNA will hybridize to the nonrepeated fraction of "accessible" DNA has been measured and compared to the extent that whole chromatin DNA will hybridize. The results show that "accessible" DNA has the same number of sequences complementary to nuclear RNA as does total DNA. In addition DNA-DNA reassociation experiments indicate that there is only a small difference between the total unique sequence populations of "accessible" and total DNA. These results indicate that nonrepeated "accessible" DNA is not preferentially transcribed in the cell as is predicted by some models of chromatin structure.

Ribosomal Genes of Xenopus laevis : Evidence of Nucleosomes in Transcriptionally Active Chromatin

“…This idea has been attractive because of its simplicity. However, much indirect evidence indicates that it may be an oversimplification of the true subtlety and complexity involved in gene regulation as it occurs in vivo (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)36). The present report extends these findings by showing that at least 60 percent of the reiterated ribosomal cistrons present in whole, undigested DNA are found protected as nucleosomes in mutant cells in which all of the genes are probably engaged in rapid rates of RNA synthesis.…”

“…The specific activity of the RNA was 1.5 x 106 count/min per microgram of RNA. The hybridization procedures and criteria were essentially as described previously (9), where the annealing conditions (0.3M NaCl, .0.03M trisodium citrate, pH 7.0, 50 percent formamide, 45°C, 16 hours of incubation) allowed for reasonably fast rates of reaction while maintaining high hybrid specificity. The low-temperature formamide hybridization conditions were those described by McConaughy et al (33).…”

“…Indirect evidence suggests that transcriptionally active (as well as inactive) chromatin may be packaged, at least partially, into the nucleosome configuration (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). In all of the studies cited, however, the starting population of cells from which the chromatin subunits were released by nuclease digestion appeared to be heterogeneous with respect to genomic transcriptional activity.…”

Assembly of DNA with histones and nonhistone chromosomal proteins in vitro

“…forming an octamer wound about a DNA of 200 base pairs, where histone FI is suggested to be on the outside of the globular subunit and it is involved in superpacking of DNA in chromatin (Oudet et al, 1975), or cross-linking between subunits in the same chromatin chain. Both the active and the inactive portion of the genome seem to be arranged in a subunit fashion (Arnold and Young, 1976). We have, therefore, sought in our studies to determine whether we could affect the structure of histone-bound DNA by various classes of salt-urea fractionated NHCP,1 thereby supporting a model for gene regulation in which certain classes of NHCP function to influence the physical structure of chromatin for transcription of various DNA sequences.…”