[Heterogeneity of the structural organization of the chromatin domain including the dihydrofolate reductase gene in Chinese hamster ovary cell culture].

We investigated histone-DNA interactions in chromatin of amplified about 1000 fold dihydrofolate reductase (DHFR) domain in methotrexate resistant Chinese hamster ovary cell line CHOC 400. We explored chromatin structure of DHFR-gene and extended region lying 3'-downstream of the DHFR-gene, which includes two zones of DNA replication initiation, Ori-beta and Ori-gamma, and matrix attachment region (MAR). Using the method of hybridization with "protein images" we found that the yield of both core histones and histone H1 cross-linked with DNA in 5'-region of the DHFR-gene, in Ori-gamma and regions flanked from either side MAR is significantly decreased in comparison with 3'-transcribed region of the DHFR-gene, Ori-beta and MAR. It was shown previously that decreased yield of histones cross-linked with DNA is typical for 5'-region of actively transcribed genes. So, histone-DNA interactions in chromatin of the 5'-region of the house-keeping and moderately transcribed DHFR-gene, Ori-gamma and regions which flank MAR resemble those in 5'-regions of actively transcribed genes. Significant differences in amount of histones cross-linked with DNA in various parts of the DHFR-domain testify to high level of heterogeneity of chromatin structure in the domain.