EMBRYONIC REGULATION OF HISTONE UBIQUITINATION IN THE SEA-URCHIN

We have used quantitative 2-D protein electrophoresis and immunoprecip itation to study the patterns of histone ubiquitination at 10 h and 36 h of embryonic development in Strongylocentrotus purpuratus. Variants csH2A, alpha H2A, beta H2A, gamma H2A, delta HA, H2AF./Z, alpha H2B, beta H2B, and gamma H2B showed up to sevenfold differences in level of monoubiquitination between variants, and individual variants showed v p to sixfold changes during development. At 36 h of embryogenesis, the late variants were less ubiquitinated than the early variants, althou gh the overall level of ubiquitination was appreciably greater than at 10 h. Antiubiquitin antibodies were used to precipitate formaldehyde- fixed chromatin fragments in order to estimate the deg ree of ubiquiti nation of the early histone genes. The 5' regulatory region of the act ive H3 gene appeared to be at least twice as ubiquitinated as the adja cent upstream spacer. However, the absolute level of ubiquitination of the early histone gene repeat seemed to be independent of transcripti onal activity. These results show that variant-specific ubiquitination of histones is a part of the developmental program in sea urchin embr yos, but is not clearly correlated with transcriptional activity of th e early histone genes, except perhaps in the regulatory regions. (C) 1 995 Wiley-Liss, Inc.