title: C-terminal phosphorylation of murine testis-specific histone H1t in elongating spermatids.
abstract: Previous studies gave differing results as to whether the testis-specific histone H1t was phosphorylated during rodent spermatogenesis. We show here that histones extracted from germ cell populations enriched with spermatids at different stages of development in rat testes reveal an electrophoretic shift in the position of H1t to slower mobilities in elongating spermatids as compared to that from preceding stages. Alkaline phosphatase treatment and radioactive labeling with (32)P demonstrated that the electrophoretic shift is due to phosphorylation. Mass spectrometric analysis of histone H1t purified from sexually mature mice and rat testes confirmed the occurrence of singly, doubly, and triply phosphorylated species, with phosphorylation sites predominantly found at the C-terminal end of the molecule. Furthermore, using collision-activated dissociation (CAD) and electron transfer dissociation (ETD), we have been able to identify the major phosphorylation sites. These include a new, previously unidentified putative H1t-specific cdc2 phosphorylation site in linker histones. The presence of phosphorylation at the C-terminal end of H1t and the timing of its appearance suggest that this post-translational modification is involved in the reduction of H1t binding strength to DNA. It is proposed that this could participate in the opening of the chromatin fiber in preparation for histone displacement by transition proteins in the next phase of spermiogenesis.
authors.affiliation: Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA.
authors.forename: Kristie L
authors.initials: KL
authors.lastname: Rose
authors.forename: Andra
authors.initials: A
authors.lastname: Li
authors.forename: Irina
authors.initials: I
authors.lastname: Zalenskaya
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Unni
authors.forename: Kim C
authors.initials: KC
authors.lastname: Hodgson
authors.forename: Yaping
authors.initials: Y
authors.lastname: Yu
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Shabanowitz
authors.forename: Marvin L
authors.initials: ML
authors.lastname: Meistrich
authors.forename: Donald F
authors.initials: DF
authors.lastname: Hunt
authors.forename: Juan
authors.initials: J
authors.lastname: Ausió
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D051381:Rats; D017386:Sequence Homology, Amino Acid; D021241:Spectrometry, Mass, Electrospray Ionization; D013087:Spermatids / Q000378:metabolism*; D013737:Testis / Q000378:metabolism*
chemical_list: D006657:Histones