Neutralization of respiratory syncytial virus by individual and mixtures of F and G protein monoclonal antibodies.

We identified several types of neutralization effected by F and G protein monoclonal antibodies (MAbs) reacted individually or as mixtures against respiratory syncytial virus (RSV). Neutralizing activity was identified by a microneutralization test in which virus replication was determined by enzyme immunoassay. Complete neutralization was seen only with MAbs against the F protein. Strain-specific neutralization, complete neutralization against some strains of RSV, and no neutralization against other strains were seen with an additional MAb against the F protein. Partial neutralization, virus replication significantly reduced but still present, and no neutralization were seen with MAbs against both the F and G proteins. Enhanced neutralization, enhanced efficacy of neutralization, or increased neutralizing titer with a mixture of two MAbs over that for the individual MAbs was seen with all MAbs against the F protein and all but three MAbs against the G protein. Most (10 of 13) of the MAbs that exhibited neutralizing activity reacted with some but not all strains of RSV in an enzyme immunoassay. The epitopes corresponding to these 10 MAbs probably contribute to the strain-specific component of the neutralizing antibody response to RSV. Our results suggest that interpretation of RSV neutralization with MAbs is complex and that studies of such neutralization should include mixtures of MAbs and multiple RSV strains.     

Deregulation of arginine biosynthesis in Synechococcus sp. PCC7942

Summary In order to deregulate arginine biosynthesis in Synechococcus sp. PCC7942, d-arginine-resistant cell lines were selected following ethyl methanesulfonate mutagenesis of wild-type (WT) cells. Three of these arginine-producing mutant (APM) cell lines, APM1, APM31 and APM40, were putative regulatory mutants based upon secretion of l-arginine into their growth medium. HPLC of lyophilized post-harvest supernatants of APM 31 and 40 resolved two predominant amino acids, arginine and citrulline. In-vitro activity of N-acetylglutamate kinase (NAGK), the proposed regulatory enzyme of the arginine pathway, was about 100-fold less sensitive to l-arginine inhibition in extracts from APM 31 and 40 than the enzyme in WT extracts. The enzyme from APM 1 was 20-fold less sensitive to l-arginine inhibition than WT. The most likely site of mutation in each of the APM cell lines is in the gene for NAGK, rendering the enzymes insensitive to l-arginine feedback control. These strains can be utilized for the phototrophic production of arginine. Offprint requests to: S. E. Bingham     

Targeted Selection Experiments and Enzyme Polymorphism: Negative Evidence for Octanoate Selection at the G6PD Locus in DROSOPHILA MELANOGASTER

Published studies have reported significant selection with respect to the G6pd locus for Drosophila melanogaster reared on Na-octanoate food. We have reexamined the selective effects of Na-octanoate on egg to adult viability with respect to the G6pd polymorphism using specially constructed X chromosomes. Four experiments were carried out using different 6Pgd backgrounds in two recombinant sets of chromosomes segregating for the G6pd locus but constructed so as to minimize variation over most of the X chromosome. In addition, two measures of viability were used, and the size of the experiments and their associated degrees of freedom are approximately double those reported in the former studies. Our results find no evidence for differential selection on G6pd genotypes (males and females) by Na-octanoate and, therefore, do not corroborate the positive results of selection reported by other investigators. The reasons for our different results are discussed.     

Quantitative ultrastructural analysis of barley sperm

Summary Complete serial ultrathin sections of seven sperm pairs, computer-assisted measurements of cell, nuclear and organelle surface areas and volumes, and three-dimensional imagery were used to demonstrate that a process of cytoplasm and organelle elimination occurs during sperm maturation in barley. The number of mitochondria per sperm cell is reduced by 50%; sperm cell surface area and volume are reduced by 30% and 51% respectively. Mean volume and surface area per mitochondrion are significantly less in mature sperms. No examples of mitochondrial fusion or degeneration were observed within sperm cells. These data, along with observations of plasma membrane apposition and vesiculation within cytoplasmic extensions containing mitochondria, support the proposition that cytoplasm and organelle loss results primarily from the formation of cytoplasmic projections that are subsequently discarded from the sperm cell body. Comparisons of the quantitative data, including the number of mitochondria, indicate that differences between sperm cells of a pair are absent to very slight. Spatial organization within the pollen grain is such that the mature sperms, as well as the sperms and vegetative nucleus, are not in close proximity.     

On the Theory of Speciation Induced by Transposable Elements

A simple methematical model describes the invasion of panmictic, sexually reproducing populations by a newly introduced transposon. The model places important constraints on the properties that transposons must have to successfully invade a population and describes the kinetics with which such an invasion will occur. Invasibility conditions serve as a basis for new, detailed scenarios whereby transposon-mediated depression in fitness produces reproductive isolation of populations. These scenarios, in turn, lead to several speculations concerning the role of transposons in evolution.