HETEROGENEITY OF CHROMATIN STRUCTURE IN THE DIHYDROFOLATE-REDUCTASE DOMAIN REVEALED USING CHINESE-HAMSTER OVARY CELL-CULTURE

A study was made of the DNA-histone interaction in the chromatin of th e DHFR gene and its 3'-untranscribed flank containing two replication origins (ori-beta and ori-gamma), and MAR. The DHFR domain was amplifi ed in cultured Chinese hamster ovary cells (CHOC 400). It was found th at in the DHFR gene 5' region, ori-gamma, and two fragments flanking M AR, there are fewer core and H1 histones linked to DNA than in the DHF R gene 3' transcribed region, ori-beta, and MAR. It has earlier been s hown that a reduced amount of DNA-linked histones is characteristic of the 5' regions of actively transcribed genes. Thus, the DHFR regions examined differ in the number of DNA-linked histones, implying that th e chromatin structure in the DHFR domain is highly heterogeneous.