Somatic mutation in the wings of Drosophila melanogaster females dysgenic due to P elements when reared at 29 degrees C.

The possibility of somatic mobilisation of P elements in Drosophila melanogaster was investigated. Flies, trans-heterozygous for the genetic markers mwh and flr3, were obtained by crossing males containing transposition-competent P elements with females having M cytotype. The hybrid dysgenic flies were reared at 29 degrees C and their wings examined for mutant clones. The frequency of mutant spots found on the wings of the female flies was significantly higher than that of female control flies. We postulate that this increase in frequency may be due to P element mobilisation at high temperature in the wing cells of dysgenic hybrids. This is in direct contrast to the large body of research which indicates that P-transposition-mediated mutation is restricted to the germline.     

Translation in vivo and in vitro of proteins resembling apoproteins of rat plasma very low density lipoprotein.

Antibodies raised against rat plasma apoVLDL and a purified fraction of arginine-rich peptides (ARP) were labeled with Na125I and were shown to bind to polyribosomes isolated from rat liver. Antibody fractions enriched by selective affinity chromatography exhibited increased levels of binding to polysomes. Anti-apoVLDL immunoreactivity was further resolved into anti-ARP and anti apoB components, each reactive with a distinct polysome population. Binding was specific for rat polysomes, and was directed toward nascent polypeptide chains. About 2% of normal rat liver polysomes were recovered by indirect immunoprecipitation with anti-apoVLDL. Ribonucleic acid (RNA) extracted from this immunoprecipitate contained species with polyadenylate (poly[A] sequences characteristic of eukaryotic messenger RNA (mRNA). These species, purified by affinity chromatography on poly(U)-Sepharose, stimulated the in vitro synthesis of immunoprecipitable apoVLDL-like proteins by about 17-fold when compared to unfractionated rat liver mRNA. Most of the in vitro translation products precipitated by purified anti-ARP migrated identically on polyacrylamide gel electrophoresis with unlabeled purified ARP. Some implications of these findings with respect to plasma VLDL biosynthesis are discussed.     

Phase transition in force during ramp stretches of skeletal muscle.

Active glycerinated rabbit psoas fibers were stretched at constant velocity (0.1-3.0 lengths/s) under sarcomere length control. As observed by previous investigators, force rose in two phases: an initial rapid increase over a small stretch (phase I), and a slower, more modest rise over the remainder of the stretch (phase II). The transition between the two phases occurred at a critical stretch (LC) of 7.7 +/- 0.1 nm/half-sarcomere that is independent of velocity. The force at critical stretch (PC) increased with velocity up to 1 length/s, then was constant at 3.26 +/- 0.06 times isometric force. The decay of the force response to a small step stretch was much faster during stretch than in isometric fibers. The addition of 3 mM vanadate reduced isometric tension to 0.08 +/- 0.01 times control isometric tension (P0), but only reduced PC to 0.82 +/- 0.06 times P0, demonstrating that prepowerstroke states contribute to force rise during stretch. The data can be explained by a model in which actin-attached cross-bridges in a prepowerstroke state are stretched into regions of high force and detach very rapidly when stretched beyond this region. The prepowerstroke state acts as a mechanical rectifier, producing large forces during stretch but small forces during shortening.     

The effects of parasitoid fecundity and host taxon on the biological control of insect pests: the relationship between theory and data

1. A simple, intuitive argument and the tenets of the biological control literature both suggest that, in general, parasitoids with a greater fecundity will provide better control of their hosts, and will thus be better biological control agents. 2. A model of host-parasitoid dynamics, based on the standard Thompson–Nicholson–Bailey approach and incorporating the effects of parasitoid fecundity-limitation and host density-dependence, also indicates that as parasitoid fecundity decreases so does local stability and the degree of host suppression. 3. A taxonomically diverse data set obtained from the biological control record failed to support this theoretical prediction, but at the same time indicated a strong effect of host taxon on the outcome of biological control. 4. The hypothesis that the fecundity of parasitoids is correlated positively with their ability to suppress host populations is supported by data exclusively from the host order Lepidoptera. 5. Possible explanations for the divergence between the fecundity-limitation hypothesis and the complete data set include: the ability of parasitoids to provide long-term control of pests without the presence of a stable host–parasitoid equilibrium; differences between the concepts of successful control in theory and practice; evolutionary trade-offs between fecundity and other parasitoid life-history features, such as search efficiency, leading to better pest control by parasitoids with low fecundity; and differing windows of vulnerability to parasitoid attack between host taxa.     

Characterization of lipoprotein produced by the perfused rhesus monkey liver

Isolated livers from rhesus monkeys (Macaca mulatta) were perfused in order to asses the nature of newly synthesized hepatic lipoprotein. Perfusate containing [3H]leucine was recirculated for 1.5 hr, followed by an additional 2.5-hr perfusion with fresh perfusate. Equilibrium density gradient ultracentrifugation clearly separated VLDL from LDL. The apoprotein composition of VLDL secreted by the liver was similar to that of serum VLDL. The perfusate LDL contained some poorly radiolabeled, apoB-rich material, which appeared to be contaminating serum LDL. There was also some material of an LDL-like density, which was rich in radiolabeled apoE. Rate zonal density gradient ultracentrifugation fractionated HDL. All perfusate HDL fractions had a decreased cholesteryl ester/unesterified cholesterol ratio, compared to serum HDL. Serum HDL distributed in one symmetric peak near the middle of the gradient, with coincident peaks of apoA-I and apoA-II. The least dense fractions of the perfusate gradient were rich in radiolabeled apoE. The middle of the perfusate gradient contained particles rich in radiolabeled apoA-I and apoA-II. The peak of apoA-I was offset from the apoA-II peak towards the denser end of the gradient. The dense end of the HDL gradient contained lipoprotein-free apoA-I, apoE, and small amounts of apoA-II, probably resulting from the relative instability of nascent lipoprotein compared to serum lipoprotein. Perfusate HDL apoA-I isoforms were more basic than serum apoA-I isoforms. Preliminary experiments, using noncentrifugal methods, suggest that some hepatic apoA-I is secreted in a lipoprotein-free form. In conclusion, the isolated rhesus monkey liver produces VLDL similar to serum VLDL, but produces LDL and HDL which differ in several important aspects from serum LDL and HDL.     

1-Thio-beta-D-galactofuranosides: synthesis and evaluation as beta-D- galactofuranosidase inhibitors

Beta-D-galactofuranosidase is a good chemotherapeutic target for the design of inhibitors, since beta-D-galactofuranose is a constituent of important parasite glycoconjugates but is not present in the host mammals. With this aim, we have synthesized for the first time alkyl, benzyl and aryl 1-thio-beta-D-galactofuranosides by condensation of penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols, in the presence of SnCl4as catalyst. The complete chemical and spectroscopical characterization of these compounds showed that the reaction was stereoselective. Debenzoylation with sodium methoxide afforded the beta-S-galactofuranosides in high yield. The thioglycosides were tested as inhibitors of the beta-D- galactofuranosidase of Penicillium fellutanum, using for the first time 4-nitrophenyl-beta-D-galactofuranoside as chromogenic substrate. The 4- aminophenyl-1-thio-beta-D-galactofuranoside, obtained by catalytic hydrogenation of the nitrophenyl derivative, was the best inhibitor being then an adequate ligand for the preparation of an affinity phase aimed at the isolation of beta-d-galactofuranosidases from different sources. Also the inhibitory activity of d-galactono-1, 4-lactone was shown.      

Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae)

Individual plants of several Amelanchier taxa contain many polymorphic nucleotide sites in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA). This polymorphism is unusual because it is not recent in origin and thus has resisted homogenization by concerted evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the result of gene flow between two major North American clades resolved by phylogenetic analysis of ITS sequences. Western North American species plus A. humilis and A. sanguinea of eastern North America form one clade (A), and the remaining eastern North American Amelanchier make up clade B. Five eastern North American taxa are polymorphic at many of the nucleotide sites where clades A and B have diverged and are thought to be of hybrid origin, with A. humilis or A. sanguinea as one parent and various members of clade B as the other parent. Morphological evidence suggests that A. humilis is one of the parents of one of the polymorphic taxa, a microspecies that we refer to informally as A. "erecta." Sequences of 21 cloned copies of the ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical to A. humilis sequence or to the clade B consensus sequence, or they are apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier "erecta" and another polymorphic taxon are suspected to be relatively old because both grow several hundred kilometers beyond the range of one of their parents. ITS sequence polymorphisms have apparently persisted in these two taxa perhaps because of polyploidy and/or agamospermy (asexual seed production), which are prevalent in the genus.