Xenopus laevis B4, an intron-containing oocyte-specific linker histone-encoding gene.

We have isolated genomic clones of the Xenopus laevis B4 gene, which encodes a linker histone, and characterized the B4 promoter. B4 mRNA is synthesized in X. laevis oocytes and disappears from the embryo by gastrulation. We find that B4 is present in only one or two copies per haploid genome and that it contains introns. Tissue-specific expression, a low copy number and presence of introns are all unusual features for vertebrate genes encoding linker histones.