Embryonic regulation of histone ubiquitination the sea urchin

We have used quantitative 2-D protein electrophoresis and immunoprecipita- tion to study the patterns of histone ubiquitination at 10 h and 36 h of embryonic development in Strongylocentrotus purpuratus. Variants csH2A, aH2A, PH2A, yH2A, SHA, H2AF./Z, aHZB, pH26, and yH2B showed up to sevenfold differences in level of monoubiquitination between variants, and individual variants showed up to sixfold changes during development. At 36 h of embryogenesis, the late variants were less ubiquitinated than the early variants, a I thoug h the overa II level of u big u itina tion was appreciably greater than at 10 h. Antiubiquitin antibodies were used to precipitate formaldehyde- fixed chromatin fragments in order to estimate the degree of ubiquitination of the early histone genes. The 5' regulatory region of the active H3 gene ap- peared to be at least twice as ubiquitinated as the adjacent upstream spacer. However, the absolute level of ubiquitination of the early histone gene re- peat seemed to be independent of transcriptional activity. These results show that variant-specific ubiquitination of histones is a part of the develop- mental program in sea urchin embryos, but is not clearly correlated with transcriptional activity of the early histone genes, except perhaps in the regula- tory regions. 0 1995 Wiley-Liss, Inc.