ABSTRACT
To investigate on the mechanisms involved in the modulation of histone gene expression during early embryogenesis of sea urchin, we determined by DNase I footprinting and electrophoretic shift analysis, the site of binding of nuclear factors to the H2A and H3 early histone genes promoters. The results showed very similar promoter binding activity in the nuclear extracts of both morula and gastrula embryos and the appearance of a developmental specific factor at gastrula stage, when the early histone genes are repressed. Furthermore, by microinjection into Xenopus laevis oocytes we showed that the gastrula extract contains repressor molecules that specifically impaired the early H2A and H3 promoters function. Finally, of the two positive transcriptional elements of the H2A modulator USE 1 and USE 2, identified by competition analysis in frog oocytes, the former seems to be involved in the activity of the H3 promoter.
