REGIONS OF THE HAPTOGLOBIN 5' FLANKING GENE SEQUENCE SHOW DIFFERENT BINDING AFFINITIES TO NUCLEAR MATRIX PROTEINS DURING THE ACUTE-PHASE RESPONSE

The effect of the acute phase response on the affinity of binding betw een nuclear matrix proteins and the rat haptoglobin (Hp) gene region w as examined. Nuclear matrices isolated from acute phase livers were en riched with the 5' Hp gene flanking region (-705/+159), but not with t he spliced, protein-coding sequence. Reassociation experiments with is olated nuclear protein matrix spheres and end-labeled fragments I (-14 6/+156), II (-146/-541), and III (-541/-705) revealed that the matrix proteins displayed an increased binding potential during the acute pha se response for all of the examined regions, this being most pronounce d for fragment II. BAL 31 digestion of fragment II showed that the seq uence element that was responsible for the increased association with nuclear matrix proteins during the acute phase response was a tract of 38 adenine bases. The DNA region established stable associations with nuclear lamin B (67 kDa, pI 5.7) in the controls, and with lamins A ( 69 kDa, pI 7.0), B, isoforms of lamin C (62 kDa, pI 6.55-6.95), and a 55-kDa (pI 5.9) polypeptide during the acute phase response. Sequence ABC (-165/-56), which overlaps fragments I and II and represents the H p cis-acting element, did not bind to the non-histone nuclear matrix p roteins.