Chromatin-specific hypersensitive sites are assembled on a Xenopus histone gene injected into Xenopus oocytes

A cloned histone H4 gene of Xenopus laevis is efficiently transcribed after injection into germinal vesicles of X. laevis oocytes. Deletion analyses indicate that less than 140 base-pairs of 5' flanking sequences and 50 base-pairs of 3' flanking sequences are required for efficient transcription of this gene in Xenopus oocytes. Chromatin footprint analysis by a direct end-label technique reveals discrete DNase I-hypersensitive and micrococcal nuclease-hypersensitive sites at the 5' and 3' boundaries of the gene, which bracket the transcribed region of this minichromosome. The specific chromatin structure assembled around this homologous gene, together with the finding that histone genes of Drosophila melanogaster are not assembled into specific nucleoprotein structures within Xenopus oocytes, strongly suggest that sequence-specific and species-specific factors may be responsible for generating the chromatin-specific hypersensitive sites at the boundaries of active genes.