Actively transcribed genes are associated with the nuclear matrix.

In the chicken oviduct, it has been well documented that steroid hormones stimulate the transcription of specific genes such as the ovalbumin gene. In addition to the presence of specific hormone receptors in the tissue, gene expression seems to require that target genes exist in large DNase I sensitive chromosomal domains. This structure appears necessary but not sufficient for transcriptional activation. In search of still other levels of control, we have investigated the interactions of genes with the nuclear matrix, a structure which has been implicated in DNA synthesis, transcription and RNA processing. Here we have isolated nuclear matrix and used a nondegradative method to fractionate nuclear DNA based on its preferential association with the matrix. The preparation was digested with a restriction enzyme and both matrix-bound and released DNAs were recovered. We found that only actively expressed genes were associated with the matrix. Furthermore, within a 100-kilobase (kb) DNase I sensitive chromosomal domain, only the transcribed regions were associated with the matrix. This association was shown to be reversible when hormone was withdrawn. Our results suggest that the nuclear matrix is the site of nuclear transcription and may represent another potential level of control for regulation of gene expression in the eukaryotic cell.