Analysis of chromatin proteins from human placenta

Low-salt extracts of chromatin from human term placenta have been examined for the presence of the high mobility group (HMG) proteins. Based upon salt-dissociation characteristics, solubilities in trichloroacetic acid and electrophoretic behaviour on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and non-equilibrium pH gradient gel electrophoresis (NEPHGE), each of the HMG proteins is present, including HMG-1, -2, -E, -14, and -17. A remarkably large amount of HMG-E is present in term human placenta. Additionally, a protein not previously recognized, which we designate HMG-PL, is present in term placenta. Electrophoretic comparison of the HMG proteins from placentae of varying gestational age, using NEPHGE, demonstrates that all of the placental HMG proteins exhibit multiplicity, reminiscent of chicken erythrocyte HMG proteins. Specifically, we found HMG-E to be unaltered in amounts relative to HMG-1 and -2 in placentae varying from 20 to 40 weeks of gestation. HMG-PL, however, is differentially expressed, increasing in amounts as gestation proceeds past 34 weeks. HMG-PL was purified and subjected to amino acid analysis. Its composition supports the notion that HMG-PL is a member of the HMG-1 family.