Sea urchin early and late H4 histone genes bind a specific transcription factor in a stable preinitiation complex

Early embryonic H4 (EH4) and H2B (EH2B) and late embryonic H4 (LH4) histone genes were transcribed in vitro in a nuclear extract from hatching blastula embryos of the sea urchin Strongylocentrotus purpuratus. The extract was prepared by slight modifications of the methods of Morris et al. (G. F. Morris, D. H. Price, and W. F. Marzluff, Proc. Natl. Acad. Sci. USA 83:3674-3678, 1986) that have been used to obtain a cell-free transcription system from embryos of the sea urchin Lytechinus variegatus. Achievement of maximum levels of transcription of the EH4 and LH4 genes required a 5- to 10-min preincubation of template with extract in the absence of ribonucleoside triphosphates. This preincubation allowed the formation of a stable complex which was preferentially transcribed compared with a second EH4 or LH4 template that was added 10 min later. Although the EH4 gene inhibited both EH4 and LH4 gene transcription in this assay and although the LH4 gene inhibited both EH4 and LH4 genes, neither of these genes inhibited transcription of the EH2B gene. Preincubation with the EH2B gene had no effect on the transcription of subsequently added EH4 or LH4 genes. Using this template commitment assay, we showed that the site of binding of at least one essential factor required for transcription of both EH4 and LH4 genes was located between positions -102 and -436 relative to the 5' terminus of the EH4 mRNA. Moreover, deletion of this region resulted in a reduction in EH4 gene transcription in vitro. The sea urchin gene-specific trans-acting factors, in the analysis of the cis-acting sequences with which they interact, and in biochemical studies on the formation of stable transcription complexes.