The High Molecular Weight Chromatin Proteins of Winter Flounder Sperm Are Related to an Extreme Histone H1 Variant

• Published in: The Journal of biological chemistry Vol. 273; no. 11; pp. 6157 - 6162
• Main Authors: Watson, C E, Davies, P L
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 13.03.1998
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Bothidae; Chromatin - chemistry; Flounder - genetics; Genomic Library; Histones - genetics; Male; Marine; Molecular Sequence Data; Pseudopleuronectes americanus; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Spermatozoa - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.11.6157

Unlike mammals, birds, and most other fishes, winter flounder completes spermatogenesis without replacing its germ cell histones with protamines. Instead, during spermiogenesis, these fish produce a family of high molecular weight (80,000–200,000) basic nuclear proteins (H M r BNPs) that bind to sperm chromatin containing the normal complement of histones. These large, basic proteins are built up of tandem iterations of oligopeptide repeats that contain phosphorylatable DNA-binding motifs. Although the H M r BNPs have no obvious homology to histones, protamines, or other sperm-specific chromatin proteins, we report here the isolation of a clone (2B) from a winter flounder genomic DNA library that establishes a link between the H M r BNPs and histone H1. The 2B sequence contains an open reading frame, which, when conceptually translated, encodes a 265-residue protein. At its N terminus the translation product contains numerous simple repeats that match the oligopeptides contained within the H M r BNPs. Unexpectedly, the C terminus of the putative protein shows 66% identity and 76% conservation to the histone H1 globular domain. This connection suggests that the H M r BNPs may have originated from the extended N-terminal tail region of a testis-specific, H1-like linker histone.