IgG or IgM monoclonal antibodies reactive with different determinants on the molecular complex bearing Lyt 2 antigen block T cell-mediated cytolysis in the absence of complement

Five rat monoclonal antibodies have been derived that express specificities for determinants present on the molecular complex bearing the Lyt 2 antigen. SDS-polyacrylamide gel electrophoresis of 125I-labeled polypeptides precipitated by each of these antibodies reveal 3 components (150,000, 75,000, and 33,000 daltons), and 2 components (44,000 and 33,000 daltons) when analyzed under nonreducing and reducing conditions, respectively. Two of these antibodies are IgG and are specific for the Lyt 2.2 determinant; the other 3 are IgM and react with determinants other than Lyt 2.2, which are nonpolymorphic. Each of the 5 antibodies can block the cytolytic activities of 5-day MLC cells or of cloned cytolytic T cells in the absence of C. Treatment of responding spleen cells with any of these antibodies and C inhibits the generation of cytolytic activity in MLC.     

Random sequences

The comparison of protein or nucleic acid sequences frequently leads to observations whose improbability can be tested only by Monte Carlo techniques that require randomizing the sequences being compared. Two decisions need to be made. One is whether one demands a resulting random sequence to have the properties of the original sequence (a shuffled sequence) or only expects it to have them (a representative sequence). The second decision concerns the properties of the sequence of which two are composition and nearest-neighbor frequencies. It is shown that biased nearest-neighbor frequencies can significantly affect the probability of observing a given result. Methods for producing random sequences according to these decisions are given.     

Correcting parsimonious trees for unseen nucleotide substitutions: the effect of dense branching as exemplified by ribonuclease

In a study of mammalian ribonuclease evolutionary rates, we applied the Fitch-Bruschi correction to reduce the bias caused by an unequal sampling of taxa in different lineages. The correction was clearly appropriate but only up to a point. The analysis showed that the sampling of taxa within the pecora was sufficiently intense that no correction for unseen, amino acid-changing, nucleotide substitutions was required. It was also found that the ribonuclease gene was duplicated at least twice at the origin of the pecoran branch of the artiodactyls.