title: Synthesis and processing of mammalian protamines and transition proteins.
abstract: Mouse and rat seminiferous tubule fragment cultures were used to examine synthesis and processing of mammalian protamines and transition proteins. The tubule fragments were incubated with [3H]-arginine, [3H]-histidine, [35S]-cysteine, or [32P]-PO4, and radiolabeled proteins were analyzed by acid/urea polyacrylamide gel electrophoresis and fluorography or autoradiography. Newly synthesized protamines were recovered from sonication-resistant nuclei (SRN) and could not be detected in cytoplasmic fractions, indicating that protamines are deposited into nuclei immediately after synthesis. Newly synthesized mouse protamine 1 (mP1) and the precursor to mouse protamine 2 (pre-mP2) migrated more slowly during electrophoresis than their predominant testicular forms, identified by staining with Coomassie blue R-250. Within 1 hour of synthesis, the electrophoretic mobilities of mP1 and pre-mP2 increased to match those of their predominant forms. These changes are consistent with initial charge-neutralizing modifications of the newly synthesized protamines, followed by removal of at least some of the modifying ligands, to unmask protamine basicity. Steady-state phosphorylation rates were high for rat protamine 1 (rP1) and were independent of phosphate content; both rP1 molecules of low and high phosphate content were rapidly phosphorylated. Pre-mP2-3, a major processing intermediate derived by proteolysis of pre-mP2, was also rapidly phosphorylated. Like the protamines, transition protein 2 (TP2) was rapidly phosphorylated and increased in electrophoretic mobility soon after synthesis. In contrast, transition protein 1 (TP1) was not phosphorylated and did not exhibit multiple electrophoretic forms.
authors.affiliation: Department of Biology, Amherst College, MA 01002.
authors.forename: G R
authors.initials: GR
authors.lastname: Green
authors.forename: R
authors.initials: R
authors.lastname: Balhorn
authors.forename: D L
authors.initials: DL
authors.lastname: Poccia
authors.forename: N B
authors.initials: NB
authors.lastname: Hecht
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000096:biosynthesis* / Q000378:metabolism; D046508:Culture Techniques; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051379:Mice; D010766:Phosphorylation; D011479:Protamines / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D012671:Seminiferous Tubules / Q000378:metabolism*; D013087:Spermatids / Q000378:metabolism
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D011479:Protamines; C053886:spermatid transition proteins; D010450:Endopeptidases