Gene, 154 (1995) 119-122 © 1995 Elsevier Science B.V. All rights reserved. 0378-1119/95/$09.50 119 GENE 08693 Dictyostelium discoideum contains a single-copy gene encoding a unique subtype of histone H1 (Genomic clone; Southern blot analysis; globular domain) Loren J. Hauser, Madhu S. Dhar and Donald E. Olins University of Tennessee, Graduate School of Biomedical Sciences, Biology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-8077, USA Received by A.-M. Skalka: 21 JurLe 1994; Revised/Accepted: 17 October/25 October 1994; Received at publishers: 8 December 1994 SUMMARY 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 eukaryetic 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. diseoideum. 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. INTRODUCTION Histone HI is believed to be the primary protein responsible for the formation and stabilization of the 30-nm chromatin fiber seen in eukaryotes (Van Holde, 1989). The HI histones of multicellular eukaryotes con- tain three domains: a shor~E basic unstructured N-terminal tail, a central globular core and a long basic unstructured C-terminal tail (Cole, 19117). Current structural models postulate that the globular domain binds to the nucleo- Correspondence to: Dr. D.E. Olins, UT-GSBMS, P.O. Box 2009, Biology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-8077 USA. Tel. (1-615) 5'74-1265; Fax (1-615) 574-1274; e-mail: olinsde@bioax1.bio.ornlgov Abbreviations: aa, amino acid(s);bp, base pair(s); cAMP-dPK, cAMP-dependent protein kinase; D., Dictyostelium; GCG, Genetics Computer Group (Madison, W I, USA); HI, histone HI protein; HI, gene (DNA, RNA) encoding HI; HPLC, high-performance liquid chromatography; kb, kilobase(s) or 1000 bp; nt, nucleotide(s); oligo, oligodeoxyribonucleotide; SDS, sodium dodecyl sulfate; SSC, 0.15 M NaC1/0.015 M Nas.citrate, pH 7.6; TFA, trifluoroacetic acid; X, any aa. some, while the two tails bind to the linker DNA between the nucleosomes (Van Holde, 1989). Histone HI does not appear to be present in Saccharomyces cerevisae (Grunstein, 1990), limiting the use of yeast as a model system to study higher-order chromatin structure and H1 function. D. discoideum (the cellular slime mold), was shown to possess histone H1 (Parish and Schmidlin, 1985). This organism is haploid during vegetative growth, contains a small genome of 5 x 107 bp (Nellen et al., 1987), has clear mitotic chromo- somes (Olins and Olins, 1993) and proceeds through a well-defined and synchronous multicellular developmen- tal pathway (Nellen et al., 1987). It is readily transformed and has a high frequency of homologous recombination (Knecht and Kessen, 1990). Hence, these properties make D. discoideum a good model system to study eukaryotic higher-order chromatin structure and function. As a step towards this goal, we report the cloning and sequence analysis of the gene for histone HI from D. discoideum. Our data show a single subtype of histone HI present as a single copy gene, in sharp contrast to other eukaryotes, SSDI 0378-1119(94)00904-X