Conformation of Moloney murine leukaemia proviral sequences in chromatin from leukaemic and nonleukaemic cells.

Abstract

THE structure of transcriptionally active and inert regions of eukaryotic chromatin can be differentiated on the basis of their sensitivity towards nuclease digestion. Whereas DNase I preferentially digests transcriptionally active genes into fragments too small to form stable hybrids, micrococcal nuclease shows no preferential digestion of specific nuclear DNA sequences1–6. We report here experiments in which the structure of Moloney murine leukaemia proviral DNA sequences in chromatin of target cells expressing the viral genome and of non-target cells in which the same sequences are repressed were examined by digestion with DNase I and microccoccal nuclease. It is shown that the Moloney murine leukaemia virus (M-MuLV) genomes in target and non-target cells of BALB/Mo mice are integrated into the host cell genome and organised in nucleosome-like structures. The difference in transcriptional activity of viral genomes in target and non-target cells is reflected by a difference in DNase I sensitivity. A partial resistance to DNase I of M-MuLV sequences in target cells suggests that the multiple viral genome copies in these cells are integrated at different sites and have different transcriptional activity.