Dictyostelium discoideum contains a single-copy gene encoding a unique subtype of histone H1

A Dictyostelium discoideum genomic library was screened using a degenerate oligodeoxyribonucleotide derived from the peptide, GPKAPT, obtained from the N terminus of purified histone H1. Two identical H1 clones were isolated. Comparative sequence data reveal a typical H1 three-domain structure with considerable homology to the globular domain of higher eukaryotic H1 histones, especially to plant H1 histones. Southern blot analysis shows that this gene is probably a single-copy gene, and suggests that any other H1 gene(s), if present, must be very different in sequence. Amino acid (aa) sequence comparison of the globular core of D. discoideum H1 to the consensus globular core reveals the absence of a 6-aa motif, GXGXXG, from D. discoideum. This motif matches the consensus for a putative nucleotide-binding loop, which is also absent in plant H1 histones like Arabidopsis thaliana, pea and wheat.