HIGH-MOBILITY GROUP PROTEIN, HMG-1, CONTAINS INSIGNIFICANT GLYCOSYL MODIFICATION

High mobility group protein-1 (HMG-1) is a ubiquitous, highly conserve d, and abundant nuclear protein. Recent findings suggest that HMG-1 ma y serve as a DNA chaperone protein and play a role in the regulation o f transcription. There is a mounting interest in elucidating the mecha nism by which HMG-1 protein takes part in these activities. HMG-1 has been reported to undergo an extensive array of posttranslational modif ications, including glycosylation. We extend the earlier findings on t he glycosylation of HMG-1 by quantitating the amount of carbohydrate o n HMG-1 from calf thymus and chicken erythrocytes isolated by 2 differ ent purification procedures. In addition, 2 different developmental st ages (embryonic and adult) were examined in the chicken erythrocytes. The glycosyl composition was quantitated using the Dionex HPAE-PAD II system. Furthermore, the presence of O-linked GlcNAc on HMG-1 was dete rmined by the enzymatic incorporation of H-3-galactose into HMG-1 prot ein. Contrary to earlier reports, less than 0.5 mol of total monosacch arides (Fuc, Man, GalNH(2), GlcNH(2), Gal) were detected per mole of H MG-1 protein, regardless of the source of the protein or the method of isolation. In addition, less than 0.002 mol of O-linked GlcNAc per mo le of HMG-1 protein was detected. Thus, insignificant amount of glycos ylation was found on HMG-1 protein. Because O-linked GlcNAc modificati on of proteins is believed to be a reversible posttranslational event, more definitive studies will need to be conducted before ruling out t hat the function of HMG-1 protein is not regulated by glycosylation.