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

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.