Analysis of mononuclear cell surfaces with fluoresceinated staphylococcal protein A complexed with IgG antibody of heat-aggregated gamma-globulin.

Fluorescein-conjugated staphylococcal protein A (SPA) was complexed with either: 1) heat-aggregated IgG, 2) B cell specific antibody, or 3) T cell specific antibody and then used for an immunofluorescent analysis of mononuclear cell surfaces. Cellular Fc receptors failed to recognize the Fc region of aggregated IgG that had been blocked by SPA. Moreover, fluoresceinated SPA that had been complexed either with anti-Fab (B-cell specific) or T cell-specific antisera prevented the nonspecific binding of these reagents to the IgG-Fc receptors on mononuclear cells, thereby permitting the latter to be properly identified as B or T lymphocytes. In addition, when unconjugated SPA was added to presensitized target cells in a test for antibody-dependent cell-mediated cytotoxicity, cytolysis was abrogated.     

Immunologic mechanisms in the pathogenesis of virus-induced murine leukemia. III. Target cell specificity of autoreactive thymocytes.

Thymocytes from preleukemic mice persistently infected with Moloney murine leukemia virus (MuLV-M-carriers) were vigorously autoaggressive toward normal syngeneic target cells; they exhibited a graded response to allogeneic cells, but they spared xenogeneic cells or syngeneic cells infected with MuLV-M or MuLV-G (Gross). Syngeneic target cells infected with nononcogenic lymphocytic choriomeningitis virus (LCMV), or transformed by the chemical carcinogen 3-methylcholanthrene were not similarly spared. This phenomenon, apparently induced by MuLV-M, is not associated with all persistent virus carrier states. Thymocytes from mice persistently infected with LCMV or with the lactic dehydrogenase virus (LDHV) failed to demonstrate an autoaggressive behavior. That transplantable lymphoma cells (derived from MuLV-M-carriers) were autoreactive in a pattern similar to thymocytes from preleukemic mice suggests a unique role for MuLV in the events leading from altered recognition of "self" to lymphoma.     

Canine erythrocyte pyruvate kinase. II. Properties of the abnormal enzyme associated with hemolytic anemia in the basenji dog

We have compared the solubility, kinetic, immunological, and electrophoretic properties of erythrocyte pyruvate kinase from normal dogs and Basenji dogs with congenital hemolytic anemia due to pyruvate kinase deficiency. Differences can be detected between the two enzymes by all methods. The enzyme from the affected animals has a greater solubility in ammonium sulfate. It has a lower K _m for phosphoenolpyruvate, while the K _m for ADP is increased. This enzyme is not inhibited by ATP or activated by fructose 1,6-diphosphate. The enzyme from the affected animals has none of the allosteric properties characteristic of the normal canine enzyme. No difference can be detected by enzyme inactivation with rabbit antiserum against the human erythrocyte enzyme, but a slight spur is observed on comparison of the two enzymes by Ouchterlony immunodiffusion. The enzymes also differ in their electrophoretic mobilities on starch gel electrophoresis.     

Partial gene duplication and posterior pituitary peptide

We have compiled the dipeptide frequencies in 100 known protein sequences. We suggest that dipeptides which occur with low frequencies can be used to locate proteins where partial gene duplication may have taken place. The 48 residue sequence of posterior pituitary peptide contains two Cys Trp pairs. The adjacent portions of the sequence are compatible with a partial gene duplication in the evolutionary history of posterior pituitary peptide.     

Aberrant DNA repair and enhanced mutagenesis following mutagen treatment of Chinese hamster Ade-C cells in a state of purine deprivation

Ade-C is a Chinese hamster ovary cell line auxotrophic for purines because of a mutation in the de novo synthetic pathway. We now show that, in the absence of exogenous hypoxanthine, replicative DNA synthesis is rapidly shut down. Various aspects of DNA repair have been studied in purine-starved cells. Incision, the first step of excision repair of UV damage, appears normal, as do the later steps, repair synthesis (demonstrated following chemical damage as well as UV-irradiation) and ligation. However, removal of UV-induced pyrimidine dimers is not detected, and it seems that the repair that occurs is aberrant. This behaviour is associated with an increase in cell killing by UV light, and a several-fold increase in the frequency of mutations induced by UV.