MATRIX ATTACHMENT REGIONS AND TRANSCRIPTION UNITS IN A POLYGENIC MAMMALIAN LOCUS OVERLAPPING 2 ISOCHORES

Eukaryotic chromosomes are punctuated by specialized DNA sequences (MA Rs) characterized by their ability to bind the network of nonhistone p roteins that form the nuclear matrix or scaffold. We previously descri bed an amplifiable cluster of genes with different tissue-specific exp ression patterns, located on Chinese hamster chromosome 1q. This model is especially appropriate to study the relationships between MARs and transcription units. We show here that four attachment regions, with sequences exhibiting motifs specific to MARs, are present within the 1 00 kb of screened DNA. Three of them are relatively short sequences lo calized in intergenic regions. The last one extends over one of the tr anscription units and contains a region previously identified as a rec ombination hot spot. Moreover, the analysis of a DNA sequence extendin g over some 50 Kb of this region and spanning at least four genes, dis closed a strikingly sharp change in G + C content. This strongly sugge sts that the studied region contains the boundary of two isochores. We propose that the frequency and the size of MARs are correlated to the ir localization in G + C rich or poor domains. J. Cell. Biochem. 67:54 1-551, 1997. (C) 1997 Wiley-Liss, Inc.