Nuclear matrix and transcriptional activity of the mouse alpha-globin gene

The association of the mouse alpha-globin gene with the nuclear matrix was studied when the gene was permanently repressed in Ehrlich ascites cells, potentially active in uninduced Friend cells or actively transcribed in induced Friend cells. Matrix-associated DNA was obtained by two methods, differing in the order of treatment of the nuclei with high salt and DNase I. By using a cloned alpha-globin probe, no enrichment in alpha-globin sequences was found in the matrix-associated DNA after DNase I digestion of high-salt treated nuclei from Ehrlich ascites and uninduced Friend cells. In induced Friend cells, a high enrichment (up to 20 times) of alpha-globin sequences was detected in the DNA left with the nuclear matrix structures. The size of the DNA fragments obtained by this procedure indicated a random attack and did not correspond to a progressive top-to-bottom cleavage model. No enrichment in alpha-globin sequences was found in induced Friend cells if nuclear matrices were obtained by DNase I digestion of the nuclei before the treatment with high salt. Our data suggest that the enrichment in actively transcribed genes of matrices from nuclei treated with high salt does not reflect a localization of these genes close to the attachment sites of the chromatin loops but rather their artefactual association with some high salt-insoluble proteins of the transcriptional complexes.