Showing papers by "Rod Balhorn published in 1999"

Protamine-Induced Condensation and Decondensation of the Same DNA Molecule

Abstract: The DNA in sperm and certain viruses is condensed by arginine-rich proteins into toroidal subunits, a form of packaging that inactivates their entire genome. Individual DNA molecules were manipulated with an optical trap to examine the kinetics of torus formation induced by the binding of protamine and a subset of its DNA binding domain, Arg6. Condensation and decondensation experiments with λ-phage DNA show that toroid formation and stability are influenced by the number of arginine-rich anchoring domains in protamine. The results explain why protamines contain so much arginine and suggest that these proteins must be actively removed from sperm chromatin after fertilization.

Cadmium concentrations in the testes, sperm, and spermatids of mice subjected to long-term cadmium chloride exposure.

Abstract: Background: Exposures to cadmium have been reported to reduce male fertility and there are several hypotheses that suggest how reduced male fertility may result from incorporation of cadmium into sperm chromatin The purpose of this study was to determine whether mice subjected to long-term intraperitoneal cadmium exposure incorporated cadmium into their sperm chromatin. Methods: Male mice were exposed to 0.1 mg/kg body weight cadmium in the form of CdCl2 via intraperitoneal injection once per week for 4, 10, 26, and 52 weeks and then sacrificed. The cadmium contents of the liver, testes, pooled sperm, and pooled spermatids from dosed and control animals were determined by atomic absorption spectroscopy. Cadmium and zinc contents in individual sperm and spermatid heads were determined by particle-induced x-ray emission. Results: Atomic absorption spectroscopy revealed that although cadmium accumulated in the liver and testes, cadmium was not detected in pooled sperm or spermatid samples down to minimum detectable limits of 0.02 μg/g dry weight. Particle-induced x-ray emission analyses did not show the presence of cadmium in any sperm or spermatid head down to minimum detectable limits of 15 μg/g dry weight. Particle-induced x-ray emission analyses also demonstrated that phosphorus, sulfur, and zinc concentrations in individual sperm and spermatid heads were not altered by exposure to CdCl2. Conclusions: Because cadmium was not incorporated into sperm chromatin at levels above 0.02 μg/g dry weight, the data cast doubt on hypotheses that suggest that reduced male fertility may result from incorporation of cadmium into sperm chromatin. Cytometry 35:30–36, 1999. Published 1999 Wiley-Liss, Inc.

Analysis of hamster protamines: primary sequence and species distribution.

Abstract: 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.