ABSTRACT
Alternating phases of DNA synthesis and mitosis, during the first 12 cell divisions of frog embryos, are driven by autonomous cytoplasmic oscillations of M-phase promoting factor (MPF). Cell-free extracts of frog eggs provide a convenient preparation for studying the molecular machinery that generates MPF oscillations and the surveillance mechanism that normally prevents entry into mitosis until chromosomal DNA is fully replicated. Early experiments suggested that unreplicated DNA blocks MPF activity by inducing phosphorylation of a crucial tyrosine residue, but recent evidence implicates a stoichiometric inhibitor (an MPF binding protein) as the 'braking' agent. Using a realistic mathematical model of the mitotic control system in frog egg extracts, we suggest that both tyrosine phosphorylation and a stoichiometric inhibitors are involved in the block of MPF by unreplicated DNA. Both pathways operate by raising the cyclin threshold for MPF activation. As a bonus, in the process of analyzing these experiments, we obtain more direct and reliable estimates of the rate constants in the model.
Subject(s)
DNA Replication/physiology , DNA/biosynthesis , Mitosis/physiology , Models, Biological , Oocytes/physiology , Animals , Female , Mathematical Computing , Oocytes/cytology , Oocytes/metabolism , XenopusABSTRACT
Bee venom specific human IgG was measured by solid phase sandwich radioimmunoassay (RIA) using bee venom adsorbed to polystyrene tubes. RIA results were found to correlate with those obtained in an enzyme immunoassay (EIA) for bee venom specific IgG. The RIA did not suffer from the high background often associated with other solid phase radioimmunoassays for human IgG. Furthermore, both the RIA and EIA were simple to perform, inexpensive and highly reproducible.
Subject(s)
Antibody Specificity , Bee Venoms/immunology , Immunoglobulin G , Absorption , Adsorption , Animals , Cattle , Humans , Immunoenzyme Techniques , Radioimmunoassay , Sheep , Temperature , Time FactorsABSTRACT
Cold-induced urticaria in a patient suffering from infectious mononucleosis is described. This condition was associated with the presence of cryoglobulins in the serum. To our knowledge this is the first description of cold-induced urticaria associated with infectious mononucleosis.
