Abstract. At a late stage of spermatogenesis in rainbow-trout testis, the entire complement of histones is replaced by newly synthesized protamine and histones are extensively phosphorylated and acetylated. Tryptic digestion of purified histones labeled by incubation of testicular cells with [32P]phosphate shows that phosphorylation occurs at a small number of seryl residues.Histone I (lysine-rich) is phosphorylated in the sequence Lys-Ser(PO4)-ProLys, which is located in the lysine-rich C-terminal region of the molecule. Histones JIb1 (slightly lysine-rich) and IV (glycine, arginine-rich) give rise to the same phosphopeptide, Ac-Ser(PO4)-Gly-Arg, which comprises the amino terminus of each histone. Thermolysin digests of phosphohistones JIb1 and IV also released a phosphopeptide with composition corresponding to the first six residues of histone IV: Ac-Ser(PO4)-Gly-Arg-Gly-Lys-Gly. An a-helical model of the N-terminal region of histone IV shows that this region is a possible DNA-binding site. Phosphorylation at serine 1 together with c-amino acetylation at lysines 5, 8, 12, and 16 (observed in histone IV from trout testis) could profoundly modify ionic interactions and lead to an "unzipping" of histone IV from DNA It is generally assumed that the high content of basic residues in the histones of eukaryote chromosomes provides the major basis for their strong binding to DNA by electrostatic interaction. Histones may be dissociated from DNA in vitro by exposure of chromatin to high ionic strengths1'2 or acidic pH,3 both of which weaken electrostatic bonds. However, these extreme conditions do not occur physiologically; the question therefore arises, are histones ever dissociated from DNA in vivo, and, if so, by what mechanisms? Spermiogenesis, the process of sperm formation and maturation, provides an unequivocal biological answer to the first question. In the spermatid cells of salmonid fishes, the entire complement of histones is progressively dissociated from DNA and replaced by a newly-synthesized sperm-specific protein, protamine.6 Possible biochemical mechanisms for removal of histones from DNA include enzymatic modification of the histones,7' 8 formation of complexes of anionic molecules with the histone,9 and perhaps also specific proteolysis of the histones in situ on the chromatin. The first possibility has been most explored and it now seems clearly established that three types of histone modification can occur: phosphorylation of the hydroxyl groups of seryl10-14 or 1616

The synthesis and enzymatic modifications of histones by phosphorylation, acetylation, and methylation during erythroid cell maturation have been studied. All newly synthesized histones, H1, H5, H2a, h2b, h3, and H4 undergo phosphorylation; histones H2a, H2b, H3, and H4, are acetylated and histones H3 and H4 are methylated. This type of histone metabolism is common to all dividing cells and therefore may be related to the assembly of histones into chromatin subunits. In the nondividing reticulocytes, the synthesis of histone H5 continues, while all the other histones show negligible incorporation of [3H]amino acids. Furthermore, the reticulocytes show a unique pattern of enzymatic modification: phosphorylation of histone H2b, acetylation of histones H2a, H2b, H3, and H4, and methylation of histones H3 and H4. These "differentiation-linked" modifications are not dependent on histone synthesis, nor related to RNA synthesis, but may be related to the reorganization of chromatin in preparation for genomic inactivation.

The sequences of both the gene and the corresponding protein of adenovirus major core protein VII have been determined. The precise location of this gene is between 43.37 and 44.90 map coordinates on the viral genome. Protein VII is 173 residues long and has a molecular weight of 19,258. Detailed analysis of its sequence has revealed four basic domains separated by several predicted a helices. It is proposed that intrachain folding of protein VII is driven by hydrophobic interactions of the a helices, leaving the basic domains of the protein to interact with DNA phosphates. Protein monomers may further associate with each other in the formation of hexameric nucleosome-like particles. The displacement and replacement of protein VII during the viral infectious cycle in the host cell appears to mimic the biology of nucleoprotamine during the processes of spermatogenesis and fertilization. The presence of a protamine-like domain affirms a hybrid histone/protamine molecular structure for protein VII, although it may resemble the protamine in function.DNA is associated with various classes of basic proteins in the nuclei of eukaryotic cells. These proteins provide structural stability as well as functional organization of the DNA into chromosomes. As an example of the different and specific roles of the nuclear proteins, full complements of somatic histones in genetically active germ-line cells are progressively replaced by the arginine-rich protamine of mature sperm (1). During the process of fertilization, protamine is removed, histones regain their associations with the DNA, and the compact chromatin of the sperm decondenses. The "life cycles" of the two classes of basic proteins in relation to the life cycle of sperm cells indicate their distinctive interactions with DNA. Among the histones, additional distinctions can be made for their role in the structure and expression of genomic DNA.The core histones, H2a, H2b, H3, and H4, are functionally different from the spacer histone, H1 (2). Because There are 1,080 copies of core protein VII (Mr = 18,000) and 180 copies of the minor core protein V (Mr = 45,000) involved in the formation of the compact virus core (6). Micrococcal nuclease digestion of the virus core has resulted in a 150-base-pair subunit DNA fragment (7), but no nucleosome repeat pattern has been observed. As early as 3 hr after infection, intranuclear adenovirus DNA assumes a nucleosomal repeat pattern similar to that of cellular chromatin (8-11). This suggests that, during virus uncoating to produce transcriptionally active viral DNA, the adenovirus 2 specific basic proteins VII and V are replaced by histones. Viral DNA synthesis, which begins at 6 hr after infection, initiates the transcription of late genes coding for viral structural polypeptides. At the late stage of infection, progeny viral DNA once again assumes the viral chromatin structure (10). The replacement of basic nuclear proteins during the growth and development of the adenovirion appears to mimic the life cycle of histones...

The signal regulatory protein (SIRP) locus encodes a family of paired receptors that mediate both activating and inhibitory signals and is associated with type 1 diabetes (T1D) risk. The NOD mouse model recapitulates multiple features of human T1D and enables mechanistic analysis of the impact of genetic variations on disease. In this study, we identify Sirpa encoding an inhibitory receptor on myeloid cells as a gene in the insulin-dependent diabetes locus 13.2 (Idd13.2) that drives islet inflammation and T1D. Compared to T1D-resistant strains, the NOD variant of SIRPα displayed greater binding to its ligand CD47, as well as enhanced T cell proliferation and diabetogenic potency. Myeloid cell–restricted expression of a Sirpa transgene accelerated disease in a dose-dependent manner and displayed genetic and functional interaction with the Idd5 locus to potentiate insulitis progression. Our study demonstrates that variations in both SIRPα sequence and expression level modulate T1D immunopathogenesis. Thus, we identify Sirpa as a T1D risk gene and provide insight into the complex mechanisms by which disease-associated variants act in concert to drive defined stages in disease progression.

During avian erythropoiesis, the blast cells of the bone marrow mature into polychromatic erythrocytes (late stages knwon as reticulocytes) and then into mature red blood cells. When chickens are made anemic, the proportion of immature cells in the anemic bone marrow increases dramatically. The level of the lysine-rich histones. H1 and H5, has been found to be constant in the blood and bone marrow of normal and anemic chickens. This implies that H5 replaces H1 quantitatively. Urea-aluminum-lactate starch gel electrophoresis of H5 from these sources show that the degree of phosphorylation of H5 is proportional to the number of immature cells. About 70% of the H5 from the most immature bone marrow is phosphorylated, while 50% of the H5 from anemic blood is phosphorylated and H5 in normal blood is almost completely devoid of phosphate. When immature cells of the anemia bone marrow are incubated in the presence of inorganic 32P and [3H]lysine and [3H]arginine, extensive 32P incorporation is found in the phospho species. A minimum of nine phosphorylated components have been demonstrated by starch gel electrophoresis. The incorporation of 3H is time dependent. After 1.5 h of labeling, 3H is found in H5 containing 0, 1, 2, and 3 phosphates. tthe combined data suggest that newly synthesized H5 becomes progressively phosphorylated and that at the terminal stage of development, the phosphorylated H5 is completely dephosphorylated. These events may be important in controlling the timing of chromatin condensation.