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

The relationship between structure and function in eukaryotic chroma-tin 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 hybrid-ize. The results show that "accessible " DNA has the same number of sequences complementary to nuclear SNA 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