Purification and characterization of the rat spermatid basic nuclear protein TP4

Adverse Effects of Nicotine on Human Sperm Nuclear Proteins

The effects of smoking on human health have long been documented. However, only a few studies have highlighted the direct effects of nicotine on sperm function. Nicotine, as a chemical compound found in tobacco, has been shown to modulate different aspects of spermatogenesis and sperm functions. Nicotine can lead to a reduction in the number of sperm, their motility and functionality. It can change the molecular expressions involved in sperm function, including genes encoding sperm nuclear proteins. The most important nuclear proteins that play a critical role in sperm function are known as H2B histone family, member W, testis-specific (H2BFWT), transition protein 1 (TNP1), transition protein 2 (TNP2), protamine-1 (PRM1), and protamine-2 (PRM2). These proteins are involved in sperm chromatin condensation, which in turn affects fertilization and embryonic development. Any alteration in the expression of these genes due to nicotine exposure/usage may lead to adverse implications in couples' fertility and the health of future generations. Since research in this area is still relatively new, it underscores the importance of understanding the potential side effects of environmental factors such as nicotine on reproductive health.

HMGB4 is expressed by neuronal cells and affects the expression of genes involved in neural differentiation

HMGB4 is a new member in the family of HMGB proteins that has been characterized in sperm cells, but little is known about its functions in somatic cells. Here we show that HMGB4 and the highly similar rat Transition Protein 4 (HMGB4L1) are expressed in neuronal cells. Both proteins had slow mobility in nucleus of living NIH-3T3 cells. They interacted with histones and their differential expression in transformed cells of the nervous system altered the post-translational modification statuses of histones in vitro. Overexpression of HMGB4 in HEK 293T cells made cells more susceptible to cell death induced by topoisomerase inhibitors in an oncology drug screening array and altered variant composition of histone H3. HMGB4 regulated over 800 genes in HEK 293T cells with a p-value ≤0.013 (n = 3) in a microarray analysis and displayed strongest association with adhesion and histone H2A –processes. In neuronal and transformed cells HMGB4 regulated the expression of an oligodendrocyte marker gene PPP1R14a and other neuronal differentiation marker genes. In conclusion, our data suggests that HMGB4 is a factor that regulates chromatin and expression of neuronal differentiation markers.

Gcse, a novel germ-cell-specific gene, is differentially expressed during meiosis and gametogenesis

Gametogenesis is a complex process wherein germ cells develop from primordial diploid cells into haploid gametes. To understand the mechanisms controlling gametogenesis, we identified a novel germ-cell-specific gene, Gcse. Gcse produces two major transcripts that are 1589 bp (Gcse-l) and 906 bp (Gcse-s) in length. Northern blotting and reverse transcription-polymerase chain reaction (RT-PCR) analyses of multiple tissues reveal that Gcse-l is expressed in both adult testes and ovaries, but Gcse-s is expressed only in adult testes. During female gonad development, Gcse-l is expressed from embryonic day 13.5 to adulthood, specifically in oocytes, and maintained in ovulated and fertilized eggs. However, Gcse-s signals were detected only in ovulated oocytes and fertilized eggs but not in adult ovary. During male gonad development, strong Gcse-l signals were detected in late pachytene spermatocytes and round spermatids. However, Gcse-s transcripts exist only in round spermatids. Furthermore, the expression of GCSE-L proteins and their subcellular localizations within cells are stage specific. GCSE-L is detected in the nucleus of late pachytene spermatocytes. During meiosis, GCSE-L is translocated to acrosome regions in spermatids and maintained in the acrosome of spermatozoa. GCSE-L colocalizes with acrosin and lectin peanut agglutinin in the Golgi apparatus. However, GCSE-S proteins are expressed only in the nucleus of spermatids. From these results, we suggest that GCSE proteins play roles in meiosis and may be involved in acrosome biogenesis during spermiogenesis.

H2A.Bbd: an X-chromosome-encoded histone involved in mammalian spermiogenesis

Despite the identification of H2A.Bbd as a new vertebrate-specific replacement histone variant several years ago, and despite the many in vitro structural characterizations using reconstituted chromatin complexes consisting of this variant, the existence of H2A.Bbd in the cell and its location has remained elusive. Here, we report that the native form of this variant is present in highly advanced spermiogenic fractions of mammalian testis at the time when histones are highly acetylated and being replaced by protamines. It is also present in the nucleosomal chromatin fraction of mature human sperm. The ectopically expressed non-tagged version of the protein is associated with micrococcal nuclease-refractory insoluble fractions of chromatin and in mouse (20T1/2) cell line, H2A.Bbd is enriched at the periphery of chromocenters. The exceedingly rapid evolution of this unique X-chromosome-linked histone variant is shared with other reproductive proteins including those associated with chromatin in the mature sperm (protamines) of many vertebrates. This common rate of evolution provides further support for the functional and structural involvement of this protein in male gametogenesis in mammals.

C-terminal phosphorylation of murine testis-specific histone H1t in elongating spermatids

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.

Biology of sperm chromatin structure and relationship to male fertility and embryonic survival

Embryonic mortality in mammals is typically thought to result from 'female factor' infertility. There is growing evidence, however, that the status of sperm chromatin (DNA) at the time of fertilisation can also influence embryonic survival. During the final stages of spermatogenesis (spermiogenesis) a number of unique biochemical, morphological and physiological processes take place that are associated with marked changes in the structure of sperm chromatin. In early stages of spermatogenesis, sperm DNA is associated with histone nucleoproteins and structured into classical nucleosome core particles similar to other somatic cells. As spermiogenesis proceeds, the histone nucleoproteins are replaced by transition proteins which are subsequently replaced by protamines. At the completion of spermiogenesis the chromatin of mature sperm has a toroidal structure that is tightly compacted and resistant to denaturation. The compaction is necessary to protect sperm chromatin during transit through the epididymis and female reproductive tract. Disruption to chromatin remodelling during spermiogenesis results in chromatin that is susceptible to denaturation. Inappropriate chromatin structure has been shown in a number of mammalian species to be related to male infertility, and specifically the failure of embryonic development. A range of techniques are available to assess chromatin status in sperm but arguably the most informative is the sperm chromatin structure assay (SCSA). The SCSA is a flow cytometric assay that uses the metachromatic properties of acridine orange to measure the susceptibility of sperm chromatin to acid-induced denaturation. A relationship has been demonstrated, primarily in men, between the SCSA outcome and the probability of continued embryonic development and the establishment of pregnancy after fertilisation. The contribution of sperm chromatin instability to reproductive wastage in both natural mating and assisted reproduction warrants further investigation as it may prove valuable as a means of decreasing the incidence of embryonic mortality. In this regard, it is possible that 'male factor' infertility may emerge as an even more important component in embryonic development.

Targeted disruption of the transition protein 2 gene affects sperm chromatin structure and reduces fertility in mice

During mammalian spermiogenesis, major restructuring of chromatin takes place. In the mouse, the histones are replaced by the transition proteins, TP1 and TP2, which are in turn replaced by the protamines, P1 and P2. To investigate the role of TP2, we generated mice with a targeted deletion of its gene, Tnp2. Spermatogenesis in Tnp2 null mice was almost normal, with testis weights and epididymal sperm counts being unaffected. The only abnormality in testicular histology was a slight increase of sperm retention in stage IX to XI tubules. Epididymal sperm from Tnp2-null mice showed an increase in abnormal tail, but not head, morphology. The mice were fertile but produced small litters. In step 12 to 16 spermatid nuclei from Tnp2-null mice, there was normal displacement of histones, a compensatory translationally regulated increase in TP1 levels, and elevated levels of precursor and partially processed forms of P2. Electron microscopy revealed abnormal focal condensations of chromatin in step 11 to 13 spermatids and progressive chromatin condensation in later spermatids, but condensation was still incomplete in epididymal sperm. Compared to that of the wild type, the sperm chromatin of these mutants was more accessible to intercalating dyes and more susceptible to acid denaturation, which is believed to indicate DNA strand breaks. We conclude that TP2 is not a critical factor for shaping of the sperm nucleus, histone displacement, initiation of chromatin condensation, binding of protamines to DNA, or fertility but that it is necessary for maintaining the normal processing of P2 and, consequently, the completion of chromatin condensation.

Abnormal spermatogenesis and reduced fertility in transition nuclear protein 1-deficient mice

Transition nuclear proteins (TPs), the major proteins found in chromatin of condensing spermatids, are believed to be important for histone displacement and chromatin condensation during mammalian spermatogenesis. We generated mice lacking the major TP, TP1, by targeted deletion of the Tnp1 gene in mouse embryonic stem cells. Surprisingly, testis weights and sperm production were normal in the mutant mice, and only subtle abnormalities were observed in sperm morphology. Electron microscopy revealed large rod-like structures in the chromatin of mutant step 13 spermatids, in contrast to the fine chromatin fibrils observed in wild type. Steps 12-13 spermatid nuclei from the testis of Tnp1-null mice contained, in place of TP1, elevated levels of TP2 and some protamine 2 (P2) precursor. Most of the precursor was processed to mature P2, but high levels of incompletely processed forms remained in epididymal spermatozoa. Sperm motility was reduced severely, and approximately 60% of Tnp1-null males were infertile. We concluded that TP1 is not essential for histone displacement or chromatin condensation. The absence of TP1 may partially be compensated for by TP2 and P2 precursor, but this dysregulation of nucleoprotein replacement results in an abnormal pattern of chromatin condensation and in reduced fertility.

Expression of a zinc-binding domain of boar spermatidal transition protein 2 in Escherichia coli

Transition protein 2 (TP2; 137 amino acid residues) from boar late spermatid nuclei has three potential zinc finger motifs in the N-terminal 34 region. Gel shift assays revealed that boar TP2 recognized a CpG island sequence in a zinc-dependent manner. However, there was some nonspecific recognition of the oligonucleotide. Then, we constructed the expression system of zinc-binding domain of TP2 (TP2Z) (residues 1-103) in Escherichia coli. Double-stranded DNA fragments encoding TP2Z were synthesized as 18 fragments with 103 residues, annealed, and cloned into the expression plasmid pET11d. TP2Z was expressed upon induction with 1 mM isopropylthiogalactoside and extracted with acid including 0.71 M 2-mercaptoethanol. TP2Z was purified by ion-exchange chromatography on Fractogel EMD SO(-)(3) and HPLC on Nucleosil 300 7C18 and on Diol-120. Atomic absorption and CD spectroscopy showed that TP2Z bound three atoms of zinc per molecule of the protein and underwent a zinc-dependent conformational change in a manner similar to that for intact TP2. Gel shift assays indicated that TP2Z recognized a CpG island sequence more specifically than intact TP2 and that the specificity is dependent on zinc.

Transition protein 4 from boar late spermatid nuclei is a topological factor that stimulates DNA-relaxing activity of topoisomerase I

Transition protein 4 (TP4) from boar late spermatid nuclei, having higher affinity for double-stranded DNA and a local melting activity of DNA, stimulated SV40 DNA-relaxing activity of eukaryotic topoisomerase I at TP4/DNA molar ratios of 6.6-11. A TP4-spermidine mixture stimulated the activity of topoisomerase I much more than spermidine alone, but no more than TP4 alone, and poly-L-arginine did not. These results suggest that TP4 contributes to the chromatin reorganization in the late spermatid nuclei from nucleosomal-type structure with negatively supercoiled DNA to nucleoprotamine structure with no supercoiled DNA.

Hyperexpression of rat spermatidal protein TP2 in Escherichia coli by codon optimization and engineering the vector-encoded 5' UTR

We have recently reported the cDNA cloning of rat spermatidal protein TP2 and its expression in Escherichia coli using pTrc 99A as the expression vector. However, the expression level was very low. We have now improved the expression of TP2 over fivefold by (1) optimizing the codons for lysine, arginine, proline, leucine, glycine, valine, threonine, alanine, and tyrosine and (2) by engineering the vector-encoded 5' UTR. The expressed protein was in the soluble phase and could be purified to homogeneity by successive chromatography on Zinc-NTA-agarose affinity matrix and heparin agarose. Serendipitously, we have also observed a concomitant hyperinduction of vector encoded beta-lactamase gene along with TP2 in the E. coli BL21 (DE3) cells.

Developmental schedule of the postnatal rat testis determined by flow cytometry

Analysis of the biochemical events and the genes expressed at various postnatal developmental stages in the testis of mammals is of great importance for understanding spermatogenesis in general and meiosis in particular. A prerequisite for such an analysis is the characterization of a detailed developmental schedule of the postnatal testis. In this study we used four-parameter flow cytometry analysis to determine a detailed testicular developmental schedule in rats as compared to mice. A dot plot of forward-scatter/side-scatter of testicular cell suspensions from mature animals revealed 7 distinct subpopulations within the testis. These, when analyzed by fluorescence parameters, were divided into 4 levels of fluorescence: cells containing 4d DNA, 2d DNA, and 2 levels of haploid cells. Observing the acquisition pattern of these subpopulations during postnatal development, we were able to suggest the following developmental schedule for the rat. At postnatal Days 6-7, the testis contains somatic cells and spermatogonia cells only. By Days 13-14, leptotene spermatocytes appear; by Days 17-18, zygotene spermatocytes are present; by Days 19-20 and Days 22-23, early and late pachytene spermatocytes, respectively, are seen. Haploid round spermatids first appear at Days 24-25 and elongating spermatids by Days 30-31; by Day 36, elongated spermatozoa can be found.

Ubiquitination of histone H3 in elongating spermatids of rat testes

Because of the potential role of histone ubiquitination in altering chromatin structure, we characterized the levels of ubiquitination of specific histones in meiotic and postmeiotic germ cells in rat testes by two-dimensional gel electrophoresis. The levels of the major ubiquitinated histone forms, mono- and poly-ubiquitinated H2A, were highest in the pachytene spermatocyte stage, declined thereafter through the round spermatid stage, and reached their lowest levels in elongating spermatids. Three additional ubiquitinated histone species, besides H2A, were detected using anti-ubiquitin antibodies specifically in the fraction enriched in elongating spermatids. Based on their electrophoretic mobilities, they corresponded to uH3, uTH3, and uH2B. Polyubiquitinated forms of these proteins were also observed. The identity of these proteins was confirmed by immunoblotting with anti-H3 antisera and by differential extraction of the proteins from the nucleus with increasing salt concentrations. This is the first report of ubiquitination of H3 in vivo. We speculate that its ubiquitination could loosen the nucleosome structure in preparation for histone removal, be a consequence of nucleosome relaxation or disruption caused by other means, or target H3 for degradation.

Nuclear basic proteins in spermiogenesis

In animal species, spermiogenesis, the late stage of spermatogenesis, is characterized by a dramatic remodelling of chromatin which involves morphological changes and various modifications in the nature of the nuclear basic proteins. According to the evolution of species, three situations can be observed: a) persistence of somatic histones or appearance of sperm-specific histones; b) direct replacement of histones by generally smaller and more basic proteins called protamines; and c) occurrence of a double nuclear basic protein transition: histones are not directly replaced by protamines but by intermediate basic proteins which are themselves replaced by one or several protamines. However, in some species, two kinds of intermediate basic proteins can be distinguished in spermatid nuclei: transition proteins and protamine precursors. Whereas transition proteins are not structurally related either to histones or to protamines, protamine precursors are further processed at the end of spermiogenesis to give rise to the mature protamine. The molecular characteristics of the protamines as well as number of protamine types present in the spermatozoon vary from species to species. In some cases, protamine-encoding genes, although present, are not expressed to a significant level. The diversity and the precise function of intermediate basic proteins remain open to discussion. Some of them are the precursors of protamines but the mechanism, sequential or not, as well as the enzyme(s) involved in the proteolytic processing, remain to be discovered.

The Drosophila don juan (dj) gene encodes a novel sperm specific protein component characterized by an unusual domain of a repetitive amino acid motif

We identified and characterized the don juan gene (dj) of Drosophila melanogaster. The don juan gene codes for a sperm specific protein component with an unusual repetitive six amino acid motif (DPCKKK) in the carboxy-terminal part of the protein. The expression of Don Juan is limited to male germ cells where transcription of the dj gene is initiated during meiotic prophase. But Western blot experiments indicate that DJ protein occurs just postmeiotically. Examination of transgenic flies bearing a dj-promoter-lacZ reporter construct revealed lacZ mRNA distribution resembling the expression pattern of the endogenous dj mRNA in the adult testes, whereas beta-galactosidase expression is exclusively present in postmeiotic germ cells. Thus, these observations strongly suggest that dj transcripts are under translational repression until in spermiogenesis. To study the function and subcellular distribution of DJ in spermiogenesis we expressed a chimaeric dj-GFP fusion gene in the male germline exhibiting strong GFP fluorescence in the liver testes, where only elongated spermatids are decorated. With regard to the characteristic expression pattern of DJ protein and its conspicuous repeat units possible functional roles are discussed.

Zinc dependent recognition of a human CpG island sequence by the mammalian spermatidal protein TP2

Rat spermatidal protein TP2 is a zinc metalloprotein with two atoms of zinc coordinated to cysteine and histidine residues and condenses alternating GC copolymer preferentially in a zinc dependent manner [Kundu, T. K., & Rao, M. R. S. (1995) Biochemistry 34,5143-5150]. In the present study, we have used a 40-mer oligonucleotide containing a human CpG island sequence to study its interaction with TP2 by gel mobility shift assays. A specific complex was observed in the presence of poly(dI).poly(dC). Preincubation of TP2 with 10 mM EDTA or 1 mM 1, 10-o-phenanthroline inhibited the complex formation by more than 90%. Competition experiments with various polynucleotides revealed the following order of efficiency: poly(dG-dC).poly(dG-dC) > cold homologous oligonucleotide > poly(dA-dT).poly(dA-dT). Homoduplexes poly(dG).poly(dC) and poly(dA).poly(dT) had no effect on the complex formation. Chromomycin A3, a GC minor groove binding drug, inhibited the complex formation. Methylation of the CpG doublet within the CpG island sequence by SssI methylase (CpG methylase) completely abolished the complex formation. Methylation of G at the N-7 position with dimethyl sulfate did not affect the recognition of CpG island by TP2. Thus, CpG islands, widely distributed in the mammalian genome, may serve as specific loci for initiation of chromatin condensation by TP2 during the later stages of spermiogenesis.

Sequence analysis of the conserved protamine gene cluster shows that it contains a fourth expressed gene

Structural data are presented on the protamine gene cluster (PGC) of human, mouse, rat, and bull. By restriction mapping we demonstrate that the organization of the protamine cluster is conserved throughout all four species, i.e., the genes are situated in a head to tail arrangement in the order: protamine 1-protamine 2-transition protein 2. Further, we established the nucleotide sequence of the entire human PGC (25 kb in total) and the 3' portion of the rat protamine cluster (PRM2 and TNP2 genes and intergenic region). In addition, a 1 kb fragment of the bovine and murine protamine cluster, situated between PRM2 and TNP2, was sequenced. This fragment is conserved regarding sequence, position, and orientation in all species examined, and was classified as likely coding region by gene recognition program GRAIL. Using the rat fragment as a probe in RNA blots, we detected a testis-specific signal of about 0.5 kb. Finally, we demonstrate a high density of Alu elements, both full and fragmented copies, in the human PGC and discuss their localization with respect to evolutionary and functional aspects.

Increased accessibility of the N-terminus of testis-specific histone TH2B to antibodies in elongating spermatids

Changes in chromatin structure during spermatogenesis were investigated using a monoclonal antibody that immunoreacts with the N-terminus of the testis-specific histone TH2B. This monoclonal antibody, which had been raised against rat tyrosine hydroxylase (TH), cross-reacted with TH2B because of sequence homology at the N-termini of TH and TH2B. The epitope was localized to the N-terminus of TH2B as trypsin-digested chromatin which lacked the N-terminal tail did not react with anti-TH and preincubating anti-TH with a synthetic peptide made from the homologous sequence between TH2B and TH inhibited its binding to TH and TH2B. In histological sections of rat testis, the primary spermatocytes and round spermatids immunoreacted weakly, whereas elongating spermatids at steps 10-12 immunoreacted intensely with anti-TH. Increased staining of elongating spermatids was also observed in mouse and hamster by immunohistochemistry. However, immunoblotting proteins extracted from separated rat testis cells showed no increase in the TH2B content of these late steps of spermatids. The apparent increase in the immunohistochemical staining corresponds to increased accessibility of the epitope in the elongating spermatids. This indicated that the N-terminus of TH2B is less tightly bound to DNA or to other proteins at this time in preparation for the removal of TH2B and other histones.

The amino acid sequence and interaction with the nucleosome core DNA of transition protein 4 from boar late spermatid nuclei

The primary structure of transition protein 4 (TP4) from boar late spermatid nuclei was determined by automated Edman degradation of S-pyridylethylated protein and of peptides generated by cleavage with Staphylococcus aureus V8 protease, lysyl endopeptidase and CNBr. Boar TP4 is a basic protein consisting of a highly basic amino-terminal half (residues 1-73) and a less basic carboxy-terminal half (residues 74-138). The latter half includes a highly hydrophobic segment, a four-times tandemly repeated sequence, N(G)QNKR(K)X, and a carboxy-terminal segment containing Trp126. Ultraviolet absorption and CD spectra of TP4-rat-liver-nucleosome-core-DNA (double-stranded DNA) complexes suggest a TP4-induced local melting of DNA. Although at 1 mM NaCl TP4 brought about a slight stabilization of the DNA against thermal melting, a destabilization of the DNA was observed at 50 mM NaCl. From the results of quenching of tryptophan (Trp126) fluorescence of TP4 upon its binding to double-stranded and single-stranded boar liver nucleosome-core DNA at 50 mM NaCl, the apparent association constants for the binding of TP4 to double-stranded and single-stranded DNA were calculated to be 7.3 x 10(3) M-1 and 4.1 x 10(3) M-1, respectively. These results suggest that TP4, having different domain structures from TP1-3 and a higher affinity for double-stranded DNA, induces a local destabilization of DNA probably through the stacking of Trp126 with nucleic acid bases.

DNA condensation by the rat spermatidal protein TP2 shows GC-rich sequence preference and is zinc dependent

Transition protein-2 (TP2), isolated from rat testes, was recently shown to be a zinc metalloprotein. We have now carried out a detailed analysis of the DNA condensing properties of TP2 with various polynucleotides using circular dichroism spectroscopy. The condensation of the alternating copolymers by TP2 (incubated with 10 microM ZnSO4), namely, poly(dG-dC).poly(dG-dC) and poly(dA-dT).poly(dA-dT), was severalfold higher than condensation of either of the homoduplexes poly(dG).poly-(dC) and poly(dA).poly(dT) or rat oligonucleosomal DNA. Between the two alternating copolymers, poly(dG-dC).poly(dG-dC) was condensed 3.2-fold more effectively than poly(dA-dT).poly(dA-dT). Preincubation of TP2 with 5 mM EDTA significantly reduced its DNA-condensing property. Interestingly, condensation of the alternating copolymer poly(dI-dC).poly(dI-dC) by TP2 was much less as compared to that of poly(dG-dC).poly(dG-dC). The V8 protease-derived N-terminal fragment (88 aa) condensed poly(dA-dT).poly(dA-dT) to a very small extent but did not have any effect on poly(dG-dC).poly-(dG-dC). The C-terminal fragment (28 aa) was able to condense poly(dA-dT).poly(dA-dT) more effectively than poly(dG-dC).poly(dG-dC). These results suggest that TP2 in its zinc-coordinated form condenses GC-rich polynucleotides much more effectively than other types of polynucleotides. Neither the N-terminal two-thirds of TP2 which is the zinc-binding domain nor the C-terminal basic domain are as effective as intact TP2 in bringing about condensation of DNA.

A haploid expressed gene cluster exists as a single chromatin domain in human sperm

Mammalian spermiogenesis is marked by the initial disruption of the nuclear-histone-DNA complex by the transition proteins for ultimate replacement with protamines. The genes for three of these low molecular weight basic nuclear proteins exist as a single linear array of PRM1, PRM2, and TNP2 on human chromosome 16p13.2. To begin to address the mechanism governing their transcriptional potentiation, a region of approximately 40 kilo-bases of the human genome encompassing these genes was introduced into the germ line of mice. Fluorescence in situ hybridization and Southern analysis showed that this segment of the human genome integrated into independent chromosomal sites while maintaining its fidelity. Transcript analysis demonstrated that the expression of the endogenous mouse protamine Prm1 and Prm2 genes as well as the mouse transition protein Tnp2 gene were expressed along with their human transgene counterparts. The pattern of expression of these transgenic human genes within this multigenic cluster faithfully represented that observed in vivo. In addition, all members of this transgenic gene cluster were expressed in proportions similar to those in human testis. Copy number-dependent and position-independent expression of the transgenic construct demonstrated that the corresponding biological locus was contained within this segment of the human genome. Furthermore, DNase I sensitivity established that in sperm the human PRM1-->PRM2-->TNP2 genic domain was contained as an approximately 28.5-kilobase contiguous segment bounded by an array of nuclear matrix associated topoisomerase II consensus sites. This is the first description of a multigenic male gamete-specific domain as a fundamental gene regulatory unit. A model of haploid-specific gene determination is presented.

Characterization of the zinc-metalloprotein nature of rat spermatidal protein TP2

Spermatidal transition protein, TP2, was purified from rat testes by Hg-affinity chromatography. The present study reports the details of the zinc-metalloprotein nature of TP2 by employing the 65 Zn-blotting technique. Chemical modification of cysteine by iodoacetic acid, and histidine by diethylpyrocarbonate, resulted in a near complete inhibition of 65Zn-binding to TP2. The 65Zinc-binding was localized to the V8 protease-derived N-terminal two-third polypeptide fragment. Circular dichroism spectroscopy studies of TP2 (zinc pre-incubated) and its V8 protease-derived polypeptide fragments revealed that the N-terminal fragment has a Type I-beta-turn spectrum, while the C-terminal fragment has a small but significant alpha-helical structure. EDTA altered the circular dichroism spectrum of TP2 and the N-terminal fragment (zinc binding domain) but not that of the C-terminal fragment.