Evolutionary relationships of the human immunodeficiency viruses

The rapid accumulation of nucleotide sequence data on viral genes has allowed, for the first time, the development of detailed phylogenies of viruses based on an objective criterion. This has been demonstrated clearly in the recent analysis of the evolutionary relationships of HIV - the AIDS virus. When first characterized, HIV seemed aberrant and almost unique in many features. Now it is known to be one of a large group of immunodeficiency viruses, which are widely distributed among primates and other mammals.     

E2 represses the late gene promoter of human papillomavirus type 8 at high concentrations by interfering with cellular factors.

The late gene promoter P7535 of the epidermodysplasia verruciformis-associated human papillomavirus type 8 (HPV8) is regulated by the viral E2 protein. Transfection experiments performed with the human skin keratinocyte cell line RTS3b and P7535 reporter plasmids revealed transactivation at low amounts and a repression of basal promoter activity at high amounts of E2 expression vector. This repression was promoter specific and correlated with the amount of transiently expressed E2 protein. Mutational analyses revealed that the negative regulation of P7535 activity is mediated by the low-affinity E2 binding site P2, which is separated by one nucleotide from the P7535 TATA box. Biochemical and genetic analyses suggested that repression is due to a displacement of the TATA-box binding protein by E2 and an interference of E2 with promoter-activating cellular factors that specifically recognize the P2 sequence. The high conservation of the P2 sequence among several papillomaviruses (epidermodysplasia verruciformis-associated HPVs, HPV1, cottontail rabbit papillomavirus, and bovine papillomavirus type 1) in the vicinity of the late gene promoter cap site suggests that an interplay of E2 and cellular factors at this sequence element is important for the expression of structural proteins.     

Determinants of Dominance in the Tree Lizard Urosaurus ornatus: the Relative Importance of Mass,Previous Experience and Coloration

A determination of some of the factors that predict the outcome of contests between male tree lizards, Urosaurus ornatus, was made using logistic regression modelling on matched-pair data. Two-day-long encounters were staged between pairs of males differing in size (snout-vent length and mass), previous contest status (previous winners and previous losers), and coloration (dorsal coloration during their previous contest and throat coloration, a fixed trait). Mass proved to be the best single predictor of contest outcome, resulting in an 80% correct classification rate for predicting winners and losers, far better than the less than 57% correct classification rate for snout-vent length. Previous social status (winner or loser) also was a powerful single predictor of contest outcome with a 793% correct classification rate, as was previous dorsal coloration (76.7%). When combined, mass and previous status produced the strongest combination of predictors with a better than 86% correct classification rate. Contrary to several previous studies, which implicated throat coloration as an important status signal of dominance, our results failed to show that throat coloration is a strong predictor of contest outcome. Possible reasons for this discrepancy with earlier findings are discussed. The logistic regression models also allow prediction of the magnitude of difference in mass between two contestants for there to be an equal chance of winning, given a second asymmetry in contest predictors.     

A new major histocompatibility complex class I b gene expressed in the mouse blastocyst and placenta

 Because of the role major histocompatibility complex (MHC) class I b molecules may play during mouse embryonic development, we thought it would be interesting to search for additional MHC class I b molecules that might be expressed in preimplantation embryos, and in particular in the trophoblastic lineage. We therefore screened a mouse preimplantation blastocyst cDNA library for MHC class I sequences. This search led to the identification and characterization of a new MHC class I b gene, blastocyst MHC. Sequences identical to the exons and 3′ untranslated region of this gene have been found in many laboratory mouse strains, as well as in the related mouse species Mus spreciligus. The presence of this gene in mouse strains of different MHC class I haplotypes argues that blastocyst MHC is a unique, newly-described gene rather than a new allele of a previously described mouse MHC class I gene. Blastocyst MHC has the structure of an MHC class I b gene, with the six exons characteristic of T-region genes. It is linked to H2-D. The amino acid sequence encoded by this gene maintains all the features of a functional antigen-presentation domain. The blastocyst MHC gene, like the human class I b gene HLA-G, is expressed at the blastocyst stage and in the placenta, and may be the mouse analog for HLA-G. Received: 31 May 1996 / Revised: 19 August 1996     

Production of δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine by entrapped ACV-synthetase fromStreptomyces clavuligerus

Summary -(l--Aminoadipyl)-l-cysteinyl-d-valine (ACV)-synthetase fromStreptomyces clavuligerus was studied under conditions that enabled the reuse of the enzyme. Coupling of ACV-synthetase to DEAE-Trisacryl and aminopropyl-glass resulted in an immobilized enzyme product of little or no catalytic activity. However, an enzyme reactor was designed by physical confinement of partially-purified ACV-synthetase in an ultrafiltration cell. This system was stimulated by phosphoenolpyruvate at lower concentrations of ATP, an effect not observed with purified enzyme. Up to 30% conversion of the limiting substrate, cysteine, to ACV occurred under semi-continuous conditions. Reaction products were investigated as potential inhibitors: AMP was the most inhibitory, but only when used at concentrations in excess of those produced in reaction mixtures. Under a nitrogen atmosphere, both product and enzyme stabilities were greatly improved and the enzyme retained 45–46% of its initial activity after five uses at room temperature during a 24-h period. Extrapolations based on these data suggest that 1.3 g partially purified enzyme (0.13 U g^–1) would be capable of producing 411 mg of ACV in a 1-L reaction mixture in this period.     

Quantitative trait locus analysis of susceptibility to diet-induced atherosclerosis in recombinant inbred mice

Quantitative trait locus (QTL) analysis is a statistical method that can be applied to identify loci making a significant impact on a phenotype. For the phenotype of susceptibility to diet-induced atherosclerosis in the mouse, we have studied four quantitative traits: area of aortic fatty streaks and serum concentrations of high-density lipoprotein-bound cholesterol (HDL-cholesterol), apolipoprotein A-I, and apolipoprotein A-II (apo A-II). QTL analysis revealed a significant locus on chromosome 1 distal impacting serum apo A-II concentration on a high-fat diet and serum HDL-cholesterol concentration on a chow diet. This locus is presumablyApoa-2, the structural gene for apo A-II. QTL analysis of aortic fatty streaks failed to reveal a significant locus.     

Genomic structure,expression and evolution of the alfalfa aspartate aminotransferase genes

Genomic clones encoding two isozymes of aspartate aminotransferase (AAT) were isolated from an alfalfa genomic library and their DNA sequences were determined. The AAT1 gene contains 12 exons that encode a cytosolic protein expressed at similar levels in roots, stems and nodules. In nodules, the amount of AAT1 mRNA was similar at all stages of development, and was slightly reduced in nodules incapable of fixing nitrogen. The AAT1 mRNA is polyadenylated at multiple sites differing by more than 250 bp. The AAT2 gene contains 11 exons, with 5 introns located in positions identical to those found in animal AAT genes, and encodes a plastid-localized isozyme. The AAT2 mRNA is polyadenylated at a very limited range of sites. The transit peptide of AAT2 is encoded by the first two and part of the third exon. AAT2 mRNA is much more abundant in nodules than in other organs, and increases dramatically during the course of nodule development. Unlike AAT1, expression of AAT2 is significantly reduced in nodules incapable of fixing nitrogen. Phylogenetic analysis of deduced AAT proteins revealed 4 separate but related groups of AAT proteins; the animal cytosolic AATs, the plant cytosolic AATs, the plant plastid AATs, and the mitochondrial AATs.     

Cells of the Upper and Lower Epidermis of Barley (Hordeum vulgare L.) Leaves Exhibit Distinct Patterns of Vacuolar Solutes

Vacuolar saps were extracted from individual, anatomically uniform cells of the upper (adaxial) and lower (abaxial) epidermis of the third leaf of barley (Hordeum vulgare L.) using a modified pressure probe. Saps (volume 80-200 pL) were sampled at various times between 3 d before and 7 d after full-leaf expansion and were analyzed for their osmolality and their concentrations of NO3-, malate, CI-, K+, and Ca2+. The osmolalities of upper and lower epidermis both increased with time but were similar to each other. In young leaves, K+ and Ca2+ were evenly distributed between the two epidermal layers, but as the leaf aged, the upper epidermis accumulated high (40-100 mM) Ca2+, whereas cells of the lower epidermis accumulated K+ instead. Nitrate concentration was 100 to 150 mM higher in the upper than in the lower epidermis, whereas CI- was 50 to 120 mM higher in the lower epidermis. These differences did not depend on the leaf developmental stage. The uneven distribution of epidermal NO3- and CI- was maintainedover a wide range of epidermal sap concentrations of these ions and was not affected by NO3- or CI- starvation or by an increase in the light intensity from 120 to 400 [mu]mol m-2 s-1. However, the latter did cause a decrease in epidermal NO3- and the appearance and accumulation of epidermal malate, particularly in the upper epidermis. The physiological implications of the results for solute storage in leaves and for the pathways of ion distribution to the epidermis are discussed.