A corrected primary sequence for bull protamine

Paternal epigenetics: Mammalian sperm provide much more than DNA at fertilization

The spermatozoon is a highly differentiated cell with unique characteristics: it is mobile, thanks to its flagellum, and is very compact. The sperm cytoplasm is extremely reduced, containing no ribosomes, and therefore does not allow translation, and its nucleus contains very closed chromatin, preventing transcription. This DNA compaction is linked to the loss of nucleosomes and the replacement of histones by protamines. Based on these characteristics, sperm was considered to simply deliver paternal DNA to the oocyte. However, some parts of the sperm DNA remain organized in a nucleosomal format, and bear epigenetic information. In addition, the nucleus and the cytoplasm contain a multitude of RNAs of different types, including non-coding RNAs (ncRNAs) which also carry epigenetic information. For a long time, these RNAs were considered residues of spermatogenesis. After briefly describing the mechanisms of compaction of sperm DNA, we focus this review on the origin and function of the different ncRNAs. We present studies demonstrating the importance of these RNAs in embryonic development and transgenerational adaptation to stress. We also look at other epigenetic marks, such as DNA methylation or post-translational modifications of histones, and show that they are sensitive to environmental stress and transmissible to offspring. The post-fertilization role of certain sperm-borne proteins is also discussed.

Dynamics of protamine 1 binding to single DNA molecules

Protamine molecules bind to and condense DNA in the sperm of most vertebrates, packaging the sperm genome in an inactive state until it can be reactivated following fertilization. By using methods that enable the analysis of protamine binding to individual DNA molecules, we have monitored the kinetics of DNA condensation and decondensation by protamine 1 (P1) and synthetic peptides corresponding to specific segments of the bull P1 DNA binding domain. Our results show that the number of clustered arginine residues present in the DNA binding domain is the most important factor affecting the condensation and stability of the DNA-protamine complex prior to the formation of inter-protamine disulfide cross-links. The high affinity of P1 for DNA is achieved by the coordinated binding of three anchoring domains, which together in bull P1 contain 19 Arg residues. The single DNA molecule experiments show that sequences containing two or more anchoring domains have an off-rate that is at least 3 orders of magnitude slower than those containing a single domain. The use of Arg, rather than Lys residues, and the inclusion of Tyr or Phe residues in the hinge regions between anchoring domains provide additional stability to the complex.

Protamine 1: protamine 2 stoichiometry in the sperm of eutherian mammals

We have compared the relative proportion of protamine 1 (P1) and protamine 2 (P2) bound to DNA in the sperm of a variety of eutherian mammals to obtain insight into how these two proteins interact in sperm chromatin. Gel electrophoresis (combined with microdensitometry) and high performance liquid chromatography (HPLC) were used to determine the content of the two protamines, and the identity of each protein was confirmed by amino-terminal sequencing or amino acid analysis. The sperm of all species examined contained P1, but P2 was found to be present only in certain species. Unlike the fixed ratio of core histones that package DNA into nucleosomes in all somatic cells, the proportion of P2 present in mature sperm was found to be continuously variable from 0 to nearly 80%. These results show that P1 and P2 do not interact with each other or DNA to form a discrete complex or subunit structure that is dependent upon particular P1/P2 stoichiometries. Data obtained from a number of closely and distantly related species also indicate that while the P2 content of sperm chromatin is allowed to vary over a wide range during the course of evolution, the relative proportion of P1 and P2 are tightly regulated within a genus.

Zinc is sufficiently abundant within mammalian sperm nuclei to bind stoichiometrically with protamine 2

Although studies have demonstrated that zinc can bind to sperm nuclear proteins, specifically protamine 2, it has not been shown that the metal is sufficiently abundant inside the sperm nucleus to interact stoichiometrically with these proteins. In this study proton-induced X-ray emission (PIXE) has been used to measure the amount of sulfur and zinc within the nuclei of individual sperm cells to infer the stoichiometry of zinc binding to protamine 2 in six species of mammal: bull, chinchilla, stallion, hamster, human, and mouse (protamine 2 comprises from 0% (bull) to 67% (mouse) of the protamine present in the sperm of these animals). Using the sulfur mass and electrophoretic data on the relative proportion of protamine 1 and protamine 2 in the sperm chromatin of these species, the protamine 1, protamine 2, and total protamine contents within each species sperm nuclei have been determined. The PIXE measurements reveal that the zinc content of the sperm nucleus varies proportionately with the protamine 2 content of sperm chromatin. PIXE analyses of hamster protamines extracted under conditions that appear to at least partially preserve zinc binding also confirm that the majority of the metal is bound to protamine. In five of the species examined, sufficient zinc is present for each protamine 2 molecule to bind one zinc. The results obtained for chinchilla sperm, conversely, indicate the chinchilla protamine 2 molecule may interact differently with zinc. Chinchilla sperm only contain enough zinc for one atom to be bound to two protamine 2 molecules.

Analysis of hamster protamines: primary sequence and species distribution

Basic nuclear proteins were isolated from the sperm of the Syrian hamster Mesocricetus auratus and characterized by gel electrophoresis, amino acid analysis, and sequencing. Analyses of the proteins by gel electrophoresis show that sperm of this species contain both protamines 1 and 2. The two proteins were purified by HPLC and the complete primary sequence of hamster protamine 1 was determined by automated amino acid sequence analysis. The protein sequence was subsequently confirmed by sequencing the PCR-amplified protamine 1 gene. The first forty-two residues of the hamster protamine 2 sequence were obtained by amino acid sequence analysis of the isolated protein, and this sequence was also confirmed and extended by sequencing the gene. Total basic nuclear protein was also isolated from sperm of six other species of hamsters, the protamines were identified by HPLC and amino acid analysis, and the proportion of protamines 1 and 2 in each species was determined. Marked differences in the protamine 2 content of sperm were observed among the different species of hamster. This variation and the high level of sequence similarity between mouse and hamster protamines provide insight into how the two protamines may be organized in sperm chromatin. Mol. Reprod. Dev. 54:273-282, 1999. Published 1999 Wiley-Liss, Inc.

AFM analysis of DNA-protamine complexes bound to mica

A novel method for reconstituting sperm chromatin was used to investigate how protamine 1 condenses DNA. Complexes formed in vitro using linearized plasmid DNA were imaged and measured by atomic force microscopy (AFM). The structures formed were found to be highly dependent on the sample preparation method used for reconstitution. Interstrand, side-by-side fasiculation of DNA and toroidal-like structures only 1-2 DNA diameters thick were observed for complexes formed in solution following direct mixing of the DNA and protamine. Large chromatin aggregates were also observed on the mica. However, if the DNA was first allowed to attach to the mica prior to addition of the protamine, well-defined toroidal complexes were formed without any observed DNA fasiculation or aggregate formation. The diameter of the toroids measured 30.6-50.2 nm (mean 39.4 nm). The dimensions of these structures indicate that the condensed DNA is stacked vertically by four to five turns, with each coil containing as little as 360-370 bp of 'B'-form DNA. This approach for preparing and imaging DNA-protamine complexes permits the analysis of intermediate structures 'trapped' on the mica as partially formed toruses of nucleoprotamine.

Evolution of protamine P1 genes in mammals

Protamine P1 genes have been sequenced following PCR amplification from 11 mammals representing five major mammalian orders: Rodentia (rat and guinea pig), Carnivora (cat and bear), Proboscidea (elephant), Perissodactyla (horse), and Artiodactyla (camel, deer, elk, moose, and gazelle). The predicted amino acid sequence for these genes together with previously reported sequences results in a data set of 25 different P1 genes and 30 different P1 amino acid sequences. The alignment of all these sequences reveals that protamines are amongst the most rapidly diverging proteins studied. In spite of the large number of differences there are conserved motifs that are also common to birds such as the N-terminal ARYR followed by the triple alternating SRSRSR phosphorylation site. The central region contains 3 arginine clusters consisting of 5-6 arginines each. The C-terminus appears to be the most variable region of the protamines. Overall the molecular evolution of P1 genes is in agreement with the expected species evolution supporting that these genes have evolved vertically.

Amino acid sequences of P1 protamines and the phylogeny of eutherian mammals: a cladistic study

Amino acid and cDNA sequences of eutherian P1 protamines, known from publications of other authors, were compared by a cladistic method. Fish, toad and bird protamines were used for the pertinent "outgroup comparisons", i.e. they provided relevant data for the comparative alignment of the sequences and for the recognition of evolutionary trends. In the sequence positions compared, each amino acid was individually assigned as a plesiomorphic or apomorphic character state (qualitative treatment). The resulting phylogenetic tree (Fig. 2) is only partially in accordance with common ideas on eutherian phylogeny. Disagreements refer to the branching points of Perissodactyla, Lagomorpha and Rodentia.

P2 protamines are phosphorylated in vitro by protein kinase C, whereas P1 protamines prefer cAMP-dependent protein kinase. A comparative study of five mammalian species

P1 protamines isolated from ejaculated human, stallion, bull, boar and ram spermatozoa and P2 protamines from human and stallion spermatozoa were subjected, after alkaline phosphatase treatment, to in vitro phosphorylation reactions using cAMP-dependent protein kinase (PKA) and protein kinase C (PKC). All P1 protamines were phosphorylated by PKA, whereas P2 protamines were phosphorylated only by PKC. In addition, human, stallion and boar, but not bull and ram, P1 protamines were phosphorylated by PKC. After phosphoamino acid analysis, the protamines showing positive signals for phosphoserine (P-Ser) were subjected to P-Ser conversion reaction and protein sequencing. Only stallion (St1) and human (HP1) P1 protamines contained P-Ser after PKA phosphorylation, located in the middle region of the molecule, i.e., at Ser29 in St1 and Ser28 in HP1. All other phosphorylated P1 protamines contained only P-Thr, which could not be further localized in the sequence with the present methods. After PKC phosphorylation, the internally located Ser residues in human (ser21) and stallion (Ser29) P1 protamines were phosphorylated and, in boar P1 protamine, only Thr43 was slightly phosphorylated. The N-terminally located Ser residues in P1 protamines, which are known to be phosphorylated in vivo, were not phosphorylated by either kinase, indicating that there must still be other types of protamine kinases in sperm cells responsible for their phosphorylation. Within P2 protamines, HP2 was equally well phosphorylated at all Ser residues in addition to some Thr phosphorylation, whereas, in St2, Ser32 was the main target for PKC phosphorylation in vitro. Collectively, PKC is a good candidate for in vivo phosphorylation of P2 protamines and PKA for phosphorylation of some hydroxyamino acid residues in P1 protamines.

Identification of the binding site of two monoclonal antibodies to human protamine

We have previously developed a number of monoclonal antibodies (Mabs) that bind to protamine. One of these antibodies, Hup1N, binds to human protamine 1 but not to protamine 2. In contrast, Mab HupA binds both protamine 1 and protamine 2. The epitopes for these two Mabs were observed to overlap, and were localized to the evolutionarily conservative amino-terminal region of protamine 1. This assignment is based on antibody binding to protamine from different species in which the protamine sequence is known, as well as analysis of antibody binding to synthetic peptides and synthetic peptides with specific amino acid substitutions.

Immunological evidence for a P2 protamine precursor in mature rat sperm

High molecular weight proteins in Rattus norvegicus that are immunoreactive with an anti-protamine 2 specific antibody but not with an anti-protamine 1 specific antibody are described. These proteins were detected by coupling high-performance liquid chromatography (HPLC) with an enzyme-linked immunosorbent assay (ELISA). Briefly, following HPLC separation of rat sperm nuclear proteins, the HPLC fractions were probed with the antibodies. We estimate that the antibody probes are 100-1000 times more sensitive than UV absorbance measurements. Immunoblot analysis following acid-urea electrophoretic separation of rat sperm nuclear proteins, and of the HPLC fractions, also detected putative protamine 2 precursor proteins. The proteins reactive with the anti-protamine 2 antibody are most likely not mature protamine 2, since they were detected in a region of the chromatogram where we would not expect protamine 2 to migrate based on the chromatographic locations of human and mouse protamine 2. Likewise, the immunoblotting experiments demonstrated that the anti-protamine 2 antibody recognized proteins with slower electrophoretic mobilities than would be expected for a mature protamine 2. An anti-protamine 1 monoclonal antibody, Hup1N, that binds rat protamine 1 is also described. Hup1N allowed for identification of the HPLC fractions that contained rat protamine 1. Finally, we demonstrated that Hup1N binds protamine 1 from a large number of species, suggesting a conserved epitope for Hup1N.

Formation of intraprotamine disulfides in vitro

When mammalian protamine is dissolved in aqueous buffers at neutral or alkaline pH, both ends of the protein fold inward toward the center of the molecule and form disulfide crosslinks that stabilize several different structures. In the absence of reducing agents, these folded forms of protamine may be visualized and quantitated by gel electrophoresis. Using this technique, we have examined the formation of bull protamine disulfides in solution and describe a variety of factors that affect this process. At pH 8, disulfide-stabilized folded forms of protamine appear within minutes after solubilization of the fully reduced protein. Five different monomers are detected by electrophoresis. Each of these monomers is stabilized by at least one disulfide crosslink and migrates with a distinct mobility, ahead of the fully reduced and extended protein. Under certain conditions, dimers of these folded structures crosslinked by interprotamine disulfides are also formed. The appearance of these disulfide-crosslinked forms of protamine is effected by air oxidation, accelerated at alkaline pH, inhibited upon lowering the pH below pH 7 and eliminated by modifying the protein's cysteine residues. Similar intramolecular disulfides are also produced after the protamine molecule binds to DNA. These results suggest that only those cysteines located within the amino- and carboxyterminal ends of the protein appear to participate in forming intramolecular disulfides in vitro.

Processing of the precursor of protamine P2 in mouse. Peptide mapping and N-terminal sequence analysis of intermediates

Protamine P2, the major basic chromosomal protein of mouse spermatozoa, is synthesized as a precursor almost twice as long as the mature protein, its extra length arising from an N-terminal extension of 44 amino acid residues. This precursor is integrated into chromatin of spermatids, and the extension is processed during chromatin condensation in the haploid cells. We have studied processing in the mouse and have identified two intermediates generated by proteolytic cleavage of the precursor. H.p.l.c. separated protamine P2 from four other spermatid proteins, including the precursor and three proteins known to possess physiological characteristics expected of processing intermediates. Peptide mapping indicated that all of these proteins were structurally similar. Two major proteins were further purified by PAGE, transferred to poly(vinylidene difluoride) membranes and submitted to automated N-terminal sequence analysis. Both sequences were found within the deduced sequence of the precursor extension. The N-terminus of the larger intermediate, PP2C, was Gly-12, whereas the N-terminus of the smaller, PP2D, was His-21. Both processing sites involved a peptide bond in which the carbonyl function was contributed by an acidic amino acid.

Nuclear transition protein 1 from ram elongating spermatids. Mass spectrometric characterization, primary structure and phosphorylation sites of two variants

The ram transition protein 1 (TP1) is present in spermatid cell nuclei in the nonphosphorylated, monophosphorylated and diphosphorylated forms. Its primary structure was determined by automated Edman degradation of S-carboxamidomethylated protein and of peptides generated by cleavage with thermolysin and endoproteinase Lys-C. The ram TP1 is a small basic protein of 54 residues and structurally very close to other mammalian TP1. The mass spectrometric data obtained from the protein and its fragments reveal that ram TP1 is indeed a mixture (approximately 5:1) of two structural variants (Mr 6346 and 6300). These variants differ only by the nature of the residue at position 27 (Cys in the major variant and Gly in the minor variant). The study of phosphorylation sites has shown that four different serine residues could be phosphorylated in the monophosphorylated TP1, at positions 8, 35, 36 or 39. From previous physical studies, it has been postulated that the Tyr32 surrounded by two highly conserved basic clusters was responsible for the destabilization of chromatin by intercalation of its phenol ring between the bases of double-stranded DNA. The presence of three phosphorylatable serine residues in the very conserved sequence 29-42 is another argument for the involvement of this region in the interaction with DNA.

Analysis of the charge distribution in the C-terminal region of histone H1 as related to its interaction with DNA

We have studied the net positive charge distribution in the C-terminal region of histone H1. We find that it is not random, but rather uniform. In most histone H1 sequences, 4 +/- 1 positive charges are found in this region of the molecule in over 95% of all possible segments that are 10 amino acids long. Neither alternating sequences (basic-nonbasic) nor more complex repeating sequences are ever found. Clusters of three or more basic amino acids are seldom observed in somatic H1s, yet their presence increases in sperm histones and even more so in protamines. It is concluded that the C-terminal region of histone H1 has a remarkably uniform distribution of charge, in spite of its apparent variations in sequence in different proteins and within individual molecules. The functional significance of these findings is discussed, suggesting a purely electrostatic role for the C-terminal region of histone H1, which may be evenly wrapped around individual segments of DNA molecules, thus decreasing its net charge. A likely candidate for a long alpha-helical region in the C-terminal region of histone H1 from sea urchin spermatozoa also has been located. This region may contribute to the aggregating properties of this histone in sperm chromatin.

Vertebrate protamine gene evolution I. Sequence alignments and gene structure

The availability of the amino acid sequence for nine different mammalian P1 family protamines and the revised amino acid sequence of the chicken protamine galline (Oliva and Dixon 1989) reveals a much close relationship between mammalian and avian protamines than was previously thought (Nakano et al. 1976). Dot matrix analysis of all protamine genes for which genomic DNA or cDNA sequence is available reveals both marked sequence similarities in the mammalian protamine gene family and internal repeated sequences in the chicken protamine gene. The detailed alignments of the cis-acting regulatory DNA sequences shows several consensus sequence patterns, particularly the conservation of a cAMP response element (CRE) in all the protamine genes and of the regions flanking the TATA box, CAP site, N-terminal coding region, and polyadenylation signal. In addition we have found a high frequency of the CA dinucleotide immediately adjacent to the CRE element of both the protamine genes and the testis transition proteins, a feature not present in other genes, which suggests the existence of an extended CRE motif involved in the coordinate expression of protamine and transition protein genes during spermatogenesis. Overall these findings suggest the existence of an avian-mammalian P1 protamine gene line and are discussed in the context of different hypotheses for protamine gene evolution and regulation.

Comparison of partial amino acid sequences of two protamine 2 variants from stallion sperm. Structural evidence that the variants are products of different genes

Protamine 1 and two protamine 2 variants were isolated from stallion sperm and separated by acetic acid-urea gel electrophoresis. After electroblotting onto polyvinyldifluoride filters, their amino-terminal amino acid sequences were determined by pulse-liquid peptide sequencing. The sequences of the two protamine 2 variants are homologous but slightly different in length and amino acid composition and indicate for the first time the existence of two different genes for this protamine species.

Primary structure of rabbit sperm protamine, the first protamine of its type with an aberrant N-terminal

Rabbit protamine was extracted from S-(pyridylethylated) sperm cell nuclei with hydrochloric acid and then isolated by reversed-phase HPLC. The primary structure was determined by amino acid sequence analysis of the total protein and of fragments obtained by digestion with endoproteinase Lys-C and thermolysin. The protamine contains 49 amino acid residues and is clearly homologous with mammalian type 1 protamines, 47% of the positions being invariant. Surprisingly, rabbit protamine possesses an N-terminal valine residue, whereas all mammalian and several non-mammalian protamine sequences of this type start with alanine, the N-terminal region being remarkably conserved during evolution.

Rat sperm protamine. Isolation and sequence analysis

Rat protamine was extracted from S-(pyridylethylated) epididymal sperm cell nuclei with dilute hydrochloric acid. The final purification was achieved by reversed-phase high-performance liquid chromatography. The primary structure was determined by N-terminal sequencing of the total S-(pyridylethylated) protein, and of endoproteinase Lys-C- and thermolysin-derived fragments. Rat protamine consists of 50 amino-acid residues. It is a typical type 1 protamine and differs in two and ten positions from the corresponding mouse and rabbit protamine, respectively. Only 26 positions are invariant in all type 1 mammalian protamines.

Sequence similarities of the protamine genes: implications for regulation and evolution

With the recent availability of the primary structural data for the trout, bovine, and mouse protamine genes, a detailed comparison of their structures has been made. This has revealed extensive conservation of potentially biologically significant regions. An inverse correlation is apparent between gene copy number and the number of sequence-distinct protamines synthesized with the number of CP-box-like (CCYPCCC) putative transcription modulating sequences situated 5' to these genes. A common nucleotide sequence 5' to the CP-box-like putative transcription modulating sequence(s) at the end of a common region has been identified. It is postulated that this is the testis-specific protamine P1 transcription regulator sequence. Evidence based on sequence similarity is also provided for the existence of a primordial protamine gene and a scheme for the evolution of vertebrate protamine genes is proposed.

Haploid-specific transcription of protamine-myc and protamine-T-antigen fusion genes in transgenic mice

The protamines are small, basic, arginine-rich proteins synthesized postmeiotically in the testes. Analysis of the regulation of synthesis of the protamine mRNA and protein is restricted by the difficulty in culturing and manipulating the cells in which transcription and translation occur. To avoid these problems, we have produced transgenic mice carrying fusion genes in which sequences 5' to the mouse protamine-2 gene have been linked to exons 2 and 3 of the mouse c-myc gene and, separately, to the simian virus 40 (SV40) early region. We show here that the prot.myc gene is correctly regulated; transcription is detected only in the round spermatids. In one family of transgenic mice carrying the 5' protamine-SV40 T-antigen fusion gene, SV40 early-region mRNA accumulated to the highest level in the testes but was also detected in the thymuses, brains, hearts, and preputial glands of the animals. Although we have demonstrated specific transcription of these fusion genes in the round spermatids, we were not able to detect the SV40 T-antigen protein.

Sequence homologies in the mouse protamine 1 and 2 genes

To identify candidates for cis-acting sequences that regulate the stage and cell-specific expression of the two coordinately regulated protamine genes in the mouse, genomic clones were isolated and the nucleotide sequences of the 5' flanking regions and coding regions were compared. Unlike most histone genes and the multigene family of trout protamine genes which are intronless, each mouse protamine gene has a single, short intervening sequence. Although the coding regions do not share significant nucleotide homology, the 5' flanking regions contain several short homologous sequences that may be involved in gene regulation. An additional shared sequence is present in the 3' untranslated region surrounding the poly(A) addition signal in both genes.

Haploid-specific transcription of protamine-myc and protamine-T-antigen fusion genes in transgenic mice

The protamines are small, basic, arginine-rich proteins synthesized postmeiotically in the testes. Analysis of the regulation of synthesis of the protamine mRNA and protein is restricted by the difficulty in culturing and manipulating the cells in which transcription and translation occur. To avoid these problems, we have produced transgenic mice carrying fusion genes in which sequences 5' to the mouse protamine-2 gene have been linked to exons 2 and 3 of the mouse c-myc gene and, separately, to the simian virus 40 (SV40) early region. We show here that the prot.myc gene is correctly regulated; transcription is detected only in the round spermatids. In one family of transgenic mice carrying the 5' protamine-SV40 T-antigen fusion gene, SV40 early-region mRNA accumulated to the highest level in the testes but was also detected in the thymuses, brains, hearts, and preputial glands of the animals. Although we have demonstrated specific transcription of these fusion genes in the round spermatids, we were not able to detect the SV40 T-antigen protein.

Aberrant protamine 1/protamine 2 ratios in sperm of infertile human males

Protamines were extracted from the sperm of fertile and infertile human males and the relative proportion of protamines 1, 2, and 3 were determined by scanning microdensitometry following electrophoresis of total protamine in polyacrylamide gels. The proportion of the three protamines was found to be similar in sperm obtained from different normal males. The distribution of protamines in sperm obtained from a select group of infertile males producing an elevated level of large sperm heads, in contrast, was different from that of the fertile males.

Mouse protamine 2 is synthesized as a precursor whereas mouse protamine 1 is not

The nuclei of mouse spermatozoa contain two protamine variants, mouse protamine 1 (mP1) and mouse protamine 2 (mP2). The amino acid sequence predicted from mP1 cDNAs demonstrates that mP1 is a 50-amino-acid protein with strong homology to other mammalian P1 protamines. Nucleotide sequence analysis of independently isolated, overlapping cDNA clones indicated that mP2 is initially synthesized as a precursor protein which is subsequently processed into the spermatozoan form of mP2. The existence of the mP2 precursor was confirmed by amino acid composition and sequence analysis of the largest of a set of four basic proteins isolated from late-step spermatids whose synthesis is coincident with that of mP1. The sequence of the first 10 amino acids of this protein, mP2 precursor 1, exactly matches that predicted from the nucleotide sequence of cDNA and genomic mP2 clones. The amino acid composition of isolated mP2 precursor 1 very closely matches that predicted from the mP2 cDNA nucleotide sequence. Sequence analysis of the amino terminus of isolated mature mP2 identified the final processing point within the mP2 precursor. These studies demonstrated that mP2 is synthesized as a precursor containing 106 amino acids which is processed into the mature, 63-amino-acid form found in spermatozoa.

Isolation and characterization of two protamines St1 and St2 from stallion spermatozoa, and amino-acid sequence of the major protamine St1

Two protamines, St1 and St2, were isolated from stallion sperm nuclei, where they represent about 75 and 25%, respectively, of the total basic protein complement. The primary structure of protamine St1 (49 residues; Mr approximately equal to 6600) has been determined. The structure of this protamine is compared to the amino-acid sequence of other mammalian protamines already known.

Monoclonal antibodies to human protamines

Nine monoclonal antibodies to human protamine, hup1a, 1b, 1c, 1d, 1e, 2a, 2b, A, and B, have been isolated and partially characterized. Enzyme-linked immunoabsorption assay analyses with HPLC-separated human protamine 1 and protamine 2+3 mixture identified five of these antibodies as specific for human protamine 1, two antibodies specific for protamine 2+3 mixture and two monoclonal antibodies reactive with all three human protamines. These findings were confirmed by immunoblotting. None of the antibodies reacted with poly-arginine or somatic histone proteins. Additional analyses with bull, boar, and ram protamines indicated that all of the monoclonal antibodies except hupA are specific for human protamine. HupA reacted with protamines from all of the species tested. These studies suggest that each of the antibodies recognizes one of at least four distinct epitopes on protamine.

Mouse protamine 2 is synthesized as a precursor whereas mouse protamine 1 is not

The nuclei of mouse spermatozoa contain two protamine variants, mouse protamine 1 (mP1) and mouse protamine 2 (mP2). The amino acid sequence predicted from mP1 cDNAs demonstrates that mP1 is a 50-amino-acid protein with strong homology to other mammalian P1 protamines. Nucleotide sequence analysis of independently isolated, overlapping cDNA clones indicated that mP2 is initially synthesized as a precursor protein which is subsequently processed into the spermatozoan form of mP2. The existence of the mP2 precursor was confirmed by amino acid composition and sequence analysis of the largest of a set of four basic proteins isolated from late-step spermatids whose synthesis is coincident with that of mP1. The sequence of the first 10 amino acids of this protein, mP2 precursor 1, exactly matches that predicted from the nucleotide sequence of cDNA and genomic mP2 clones. The amino acid composition of isolated mP2 precursor 1 very closely matches that predicted from the mP2 cDNA nucleotide sequence. Sequence analysis of the amino terminus of isolated mature mP2 identified the final processing point within the mP2 precursor. These studies demonstrated that mP2 is synthesized as a precursor containing 106 amino acids which is processed into the mature, 63-amino-acid form found in spermatozoa.