EN
A glycoprotein purified from the internal nuclear matrix of chicken liver nuclei has been identified, by partial sequencing and by Western blotting, as hsp108, which is a component of the hsp90 superfamily. This protein has been previously characterized as a protein which copurifies with the cytoplasmic progesterone receptor and as a transferrin-binding protein of the chicken oviduct cell membrane. We have found that hsp108 is present in the nuclear matrix even in the absence of a heat shock or of other noxious conditions. Some of the properties already described for its homologous proteins (endoplasmin, grp94, hsp100) might explain its function at the nuclear matrix level. Hsp108 isolated from the liver nuclear matrix has a carbohydrate composition significantly different from that of the protein of the oviduct cell membrane.