We have previously identified a class of DNA sequence elements, termed matrix association regions (MARs), which specifically bind to nuclear matrices in vitro and are believed to be at the bases of chromosomal loops in vivo. Here we demonstrate that nuclear matrices prepared from the yeast Saccharomyces cerevisiae will specifically bind an MAR sequence derived from the mouse kappa light chain immunoglobulin gene. This suggests that both MAR sequences and their binding sites have been strongly evolutionarily conserved.