CHICKEN MAR BINDING-PROTEIN P120 IS IDENTICAL TO HUMAN HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN (HNRNP)-U

We have previously identified two proteins from chicken oviduct nuclei that specifically bind to matrix/scaffold attachment regions (MARs/SA Rs). Here one of these proteins, named p120 due to its apparent molecu lar weight, is purified to near homogeneity and shown to be identical to a previously described component of heterogeneous nuclear ribonucle oprotein particles, hnRNP U, on the basis of amino acid sequence analy sis of tryptic peptides. p120 binds to multiple MAR fragments provided they have a minimal length of approximately 700 bp. Binding of MAR fr agments is specifically competed by homoribopolymers poly(G) and poly( l), which form four-stranded structures. Our results suggest that p120 /hnRNP U may serve a dual function, first as a component of hnRNP part icles, and second as an element in the higher-order organization of ch romatin.