Chromosomes Protamines

In mammals the histones are removed and replaced by transition basic proteins in mid-spermatids and then the transition basic proteins are replaced by protamines in late spermitids and sperm [119]. In mouse and rat sperm, histones removal is complete or nearly so [119,120], but in humans 15% of the DNA remains associated with histones [121]. In bovine sperm more than 99% of the histones are removed, but CENP-A is quantitatively retained [122]. This retained CENP-A could be part of an epigenetic mark that allows the positions of the centromeres to be retained in sperm and on the paternal chromosomes of the zygote. 

Histones are closely related to protamines and occur in the chromosomes of organs with genuine cell nuclei, that is, for example, the thymus glands. Their biological significance is largely unknown. Apparently, they regulate replication or transcription (see further, below). 

Nucleoprotein heteropolar complexes of nucleic acids (in particular, nuclear DNA) with basic, acid-soluble proteins (histones or protamines), and with acidic, base- or detergent-soluble non-histone chromatin proteins. N. occur mainly in the chromatin of the cell nucleus in its quiescent state, and in the chromosomes when the nucleus is active, i.e. dividing. Many viruses consist entirely of N., but N. are absent from bacteria. N. are concerned in DNA replication, and in the control of gene function during protein biosynthesis. 

Chromatin and chromosomes are composed mainly of DNA, RNA and numerous proteins. Important enzyme proteins are DNA-polymerase for DNA-repli-cation, and RNA-poIymerase for transcription. Other chromosomal proteins (histones, protamines and acidic proteins) are engaged in the regulation of replication and transcription (see Chromosomes). 

Two-dimensionai gel electrophoresis of histones from interphase and mitotic cells treated with dimethyl sulfate. 2-D gel electrophoresis was carried out with proteins separated by nonequilibrium pH gradient electrophoresis in the first dimension and on 8% polyacrylamide slab gels in the second (6, 7). Separation of histones was enhanced by use of a urea solubilization buffer containing protamines to displace histones from DNA (8). The resulting autoradiograms for histones of both nuclei and chromosomes are in Fig. 3. Incubation of mitotic cells with [32P]NAD before chromosomes were isolated led to prominent labeling of histones H2B and H4 (A, B), and spots are also visible at the positions of HIA and HIB. 32p incorporation is also seen at the positions of histones H2A and H3. hi Fig. 3B, a similar pattern is observed for chromosomal histones from cells treated with DMS. The primary acceptors of isotope are H2B and H4, with radioactivity also present at the positions of HIA, HIB, H2A, and H3. A major change in the relative distribution of 32p between species is clearly not a feature of DMS treatment. 

Fig. 3. Histones, resolved by two-dimensional gel electrophoresis, from cells treated with DMS. [ pjNAD-labeled nuclei and chromosomes were isolated, and the histones were solubilized in protamine-containing buffer (8). Autoradiograms (A) of control chromosomes and (B) from cells treated with 1.0 mM DMS (C) labeled histones of control nuclei and (D) nuclei from DMS-treated (1.0 mM) cells. The isoelectric focusing dimension (horizontal) used nonequilibrium pH gradient electrophoresis. SDS-polyacrylamide slab gels (12.5%) were run in the second dimension (vertical).

The Chemistry of the Chromosome 88 Chromosomal Proteins 88 Protamines Histones... 

There are at least three types of chromosomal proteins histones, protamines, and residual proteins [58-63]. It has been estimated that the nuclear histones represent 90-92% of the total protein in the chromosome. The remaining portion (8-10%) is composed of the residual protein, or non histone proteins. 

The nucleoproteins of the nuclei of trout, salmon and herring sperm, are made up almost entirely of protamine and desoxyribonucleic acid. The nucleoproteins of thymus are made up of desoxyribonucleic acid (40%), ribonucleic acid (1-2%), histones and non-basic proteins. The cellular nuclei contain chiefly desoxyribonucleic acid but, in addition, there is a little ribonucleic acid (in the nucleolus and chromosomes). The cytoplasmic nucleoproteins in general contain only ribonucleic add assodated with proteins which do not have the basic properties of those joined to desoxyribonucleic acid. But the reproductive cell of animals (oocytes) contain desox5rribonudeic add in the cytoplasm. The desoxyribonucleic add of the chromosomes is combined with histones, protamines, and a protein of the usual t3rpe, which is referred to as residual protein. 

Chemical Characteristics of Histones and Protamines and the Nature of Their Complexes with DNA in the Chromosomes... 

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