Eukaryotic chromatin is organized into looped domains formed by attachment of specific DNA sequences (termed MARs or SARs) to network of nuclear proteins (nuclear matrix). We have looked for matrix attachments within 4.9 kb DNA region encompassing rat hsp70.1 gene. Sequences that flank both 3'-end and 5'-end of the gene contain motifs characteristic for MAR/SARs identified in numerous other genes. These flanking sequences formed in vitro complexes with proteins of the nuclear matrix from different rat tissues. Using Southwestern analysis we showed that similar matrix proteins interacted with sequences flanking rat hsp70.1 gene and established MAR from mouse kappa immunoglobulin gene.