High mobility group proteins 1 and 2 are present in simian virus 40 provirions, but not in virions

Viral particles at the late stages of SV40 morphogenesis were examined for the presence of HMG proteins 1 and 2, by an immunochemical method involving the transfer of proteins from polyacrylamide gels to nitrocellulose membranes. It was found that these proteins are present in SV40 provirions, in which histone H1 is still associated with viral chromatin, but absent in mature SV40 virions.

Solid phase radioimmunoassay for chromosomal components

This manuscript describes the use of a solid phase radioimmunoassay for serological analysis of chromosomal components. The applicability of this assay for various studies on nonhistone chromosomal proteins, histones, and chromatin subunits is illustrated. By this technique it is possible to detect and quantify nuclear antigens in the nanogram range. The assay has all the inherent sensitivity and precision of radioimmunoassays and, as such, introduces a new, convenient method for serological analyses of chromosomal components. The results presented reconfirm the serological similarity among the HMG (high mobility group) proteins derived from various sources. The amount of HMG proteins present in mononucleosomes purified from calf thymus is similar to that present in mononucleosomes purified from HeLa cells, suggesting that various tissues contain similar amounts of these proteins. Per nucleosome, dinucleosomes and trinucleosomes contain as much HMG-1 protein as mononucleosomes, suggesting that the protein is not exclusively associated with those regions of DNA which have been solubilized by micrococcal nuclease. Part of the antigenic determinants present in HMG-1 forming a complex in the nucleosomal conformation do not interact with antibodies.

Serological analysis of species specificity in the high mobility group chromosomal proteins

The non-histone chromosomal protein of the high mobility group (HMG-1) present in mouse liver was purified to homogeneity. Antibodies against this protein as well as pure HMG-1 derived from calf thymus and HMG-E purified from duck erythrocytes were elicited in rabbits. The interaction between the antibodies and the immunogens was measured by passive hemoagglutination and by quantitative microcomplement fixation. Quantitative microcomplement fixation assays revealed that the immunological distance between HMG-1 from calf thymus and HMG-1 from mouse liver and duck erythrocytes was 15. This corresponds to 3% sequence differences. It was estimated that amino acid substitution occurred at about seven positions in the polypeptide chain. Thus, HMG-1 proteins display remarkable evolutionary conservation in their primary sequence, similar to that displayed by histones H4 and H3, suggesting that their biological function is dependent on stringent structural requirements. HMG-E protein is significantly different from both HMG-1 and HMG-2 derived from calf thymus. As such, it is a protein unique to avian erythrocytes.

Life history of mouse sperm protein. Intratesticular stages

A basic protein fraction, migrating as a single band in acetic acid-urea gel, distinct from histones, was isolated from mouse sperm collected from vasa deferentia and caudae epididymides and was used to immunize female rabbits. The presence of antibodies to the mouse sperm protein (MSP) in the rabbit antisera was demonstrated by a cytoimmunofluorescence procedure using the cells of origin of the antigenic protein, the mature mouse sperm. The specificity of the antisera was verified by fluid and gel precipitation tests and by crossed immunoelectrophoresis. The latter procedure demonstrated the presence of two antigen-antibody systems, consonant with earlier reports that the basic chromosomal protein of mouse sperm is heterogeneous. MSP antigen in situ was recognized by the specific antibodies of the rabbit antisera only after the smear of mature sperm was treated with either of two reducing agents: 2-mercaptoethanol or dithiothreitol. However, when the immunofluorescence procedure was applied to untreated smears of mouse testicular cells, spermatids of all stages from 1 to 14-15 were positive, while spermatocytes, stage 16 spermatids and spermatozoa were negative. After treatment of testes smears with reducing agent, only spermatocytes remained negative. Those observations indicate the following: (a) MSP is immunogenic in a heterologous species; (b) its antigenic sites are detectable in spermatozoa and spermatids of all stages, but not in primary spermatocytes; (c) those antigenic sites become masked at about stage 15 of spermiogenesis and may be unmasked by treatment with a reducing agent. The interpretation is made, therefore, that one or more components of MSP are assembled at the beginning of spermiogenesis and undergo an alteration in the final intratesticular stage of spermatid maturation. That alteration may be presumed to be the formation of disulfide linkages between the cysteine residues.