Photocrosslinking locates a binding site for the large subunit of human replication protein A to the damaged strand of cisplatin-modified DNA.

The repair proteins XPA, XPC and replication protein A (RPA) have been implicated in the primary recognition of damaged DNA sites during nucleotide excision repair. Detailed structural information on the binding of these proteins to DNA lesions is however lacking. We have studied the binding of human RPA (hRPA) and hRPA-XPA-complexes to model oligonucleo-tides containing a single 1, 3-d(GTG)-cisplatin-modification by photocrosslinking and electrophoretic mobility shift experiments. The 70 kDa subunit of hRPA can be crosslinked with high efficiency to cisplatin-modified DNA probes carrying 5-iodo-2"-deoxyuridin (5-IdU) as crosslinking chromophore. High efficiency crosslinking is dependent on the presence of the DNA lesion and occurs preferentially at its 5"-side. Examination of the crosslinking efficiency in dependence on the position of the 5-IdU chromophore indicates a specific positioning of hRPA with respect to the platination site. When hRPA and XPA are both present mainly hRPA is crosslinked to the DNA. Our mobility shift experiments directly show the formation of a stable ternary complex of hRPA, XPA and the damaged DNA. The affinity of the XPA-hRPA complex to the damaged DNA is increased by more than one order of magnitude as compared to hRPA alone.     

Synergistic antiallergic activity of combined histamine H1- and cysteinyl leukotriene1-receptor blockade in human bronchus.

Mast cell histamine (HA) and cysteinyl leukotrienes (CysLT) account for most of the early phase bronchospasm in asthma. However, activation of the smooth muscle CysLT1-receptor plays a major role in asthmatic bronchospasms. CysLT-receptor antagonists or CysLT-synthesis inhibitors are efficacious in asthma but do not completely abolish asthmatic bronchospasms. A recent clinical study showed that combined antagonists loratadine (H1) and zafirlukast (CysLT1) were more effective against allergic bronchospasms than either drug alone. We examined the combined efficacy of H1- and CysLT1-receptor antagonists in allergic human bronchus. The H1- and CysLT1-receptor antagonists chlorpheniramine (CTM; 1 microM) and MK-571 (0.03 microM), were tested alone and in combination, against anti-human IgE antibody (Ab)-induced contractions of passively sensitized isolated human bronchus. Ab-induced allergic contractions were reduced 15% and 36% by CTM (1 microM) and MK-571 (0.03 microM), respectively. Combined CTM (1 microM) and MK-571 (0.03 microM) significantly inhibited the Ab response by 87%. Mechanistic investigations in isolated human bronchus and cultured human cord blood mast cells suggest that H1- and CysLT-receptor interactions likely occur at the airway smooth muscle level. CTM and MK-571 synergistically inhibited human allergic bronchospasm in the present in vitro model. The mechanism underlying this synergistic activity requires further investigation.     

Estimating Ancestral Population Parameters

The expected numbers of different categories of polymorphic sites are derived for two related models of population history: the isolation model, in which an ancestral population splits into two descendents, and the size-change model, in which a single population undergoes an instantaneous change in size. For the isolation model, the observed numbers of shared, fixed, and exclusive polymorphic sites are used to estimate the relative sizes of the three populations, ancestral plus two descendent, as well as the time of the split. For the size-change model, the numbers of sites segregating at particular frequencies in the sample are used to estimate the relative sizes of the ancestral and descendent populations plus the time the change took place. Parameters are estimated by choosing values that most closely equate expectations with observations. Computer simulations show that current and historical population parameters can be estimated accurately. The methods are applied to DNA data from two species of Drosophila and to some human mitochondrial DNA sequences.     

Production of Leptin inEscherichia coli:A Comparison of Methods

A procedure is described for gram-scale refolding ofEscherichia coli-derived human leptin inclusion bodies. Refolding was achieved by gradually reducing denaturant using a diafiltration method. Refolded leptin is characterized byin vivomodulation of food intake, reduction in body weight, and lowering of insulin and glucose levels inob/obmice. In addition, refolded leptin is characterized by radioimmunoassay (RIA) and activation of the leptin receptor in a cell-based assay. For comparison we also refolded leptin by a simple dilution method and produced periplasmic derived leptin, which did not requireex vivofolding. Leptin produced by these three methods and leptin obtained from commercial sources were compared using the RIA and the cell-based assay and appeared to be of comparable quality and potency.     

Maize ribosome-inactivating protein (b-32). Homologs in related species, effects on maize ribosomes, and modulation of activity by pro-peptide deletions.

The ribosome-inactivating protein (RIP) from maize (Zea mays L.) is unusual in that it is produced in the endosperm as an inactive pro-form, also known as b-32, which can be converted by limited proteolysis to a two-chain active form, alpha beta RIP. Immunological analysis of seed extracts from a variety of species related to maize showed that pro/alpha beta forms of RIP are not unique to maize but are also found in other members of the Panicoideae, including Tripsacum and sorghum. Ribosomes isolated from maize were quite resistant to both purified pro- and alpha beta maize RIPs, whereas they were highly susceptible to the RIP from pokeweed. This suggests that the production of an inactive pro-RIP is not a mechanism to protect the plant's own ribosomes from deleterious action of the alpha beta RIP. RIP derivatives with various pro-segments removed were expressed at high levels in Escherichia coli. Measurement of their activity before and after treatment with subtilisin Carlsberg clearly identified the 25-amino acid intradomain insertion, rather than the N- or C-terminal extensions, as the major element responsible for suppression of enzymatic activity. A RIP with all three processed regions deleted had activity close to that of the native alpha beta form.     

DNA Sequence Variation at the Period Locus within and among Species of the Drosophila Melanogaster Complex

A 1.9-kilobase region of the period locus was sequenced in six individuals of Drosophila melanogaster and from six individuals of each of three sibling species: Drosophila simulans, Drosophila sechellia and Drosophila mauritiana. Extensive genealogical analysis of 174 polymorphic sites reveals a complex history. It appears that D. simulans, as a large population still segregating very old lineages, gave rise to the island species D. mauritiana and D. sechellia. Rather than considering these speciation events as having produced ``sister' taxa, it seems more appropriate to consider D. simulans a parent species to D. sechellia and D. mauritiana. The order, in time, of these two phylogenetic events remains unclear. D. mauritiana supports a large number of polymorphisms, many of which are shared with D. simulans, and so appears to have begun and persisted as a large population. In contrast, D. sechellia has very little variation and seems to have experienced a severe population bottleneck. Alternatively, the low variation in D. sechellia could be due to recent directional selection and genetic hitchhiking at or near the per locus.     

Cholesterol Esters of the Human Brain During Fetal and Early Postnatal Development: Content and Fatty Acid Composition

Abstract: The content and fatty acid composition of cholesterol esters of the human brain during development from 13 weeks' gestation up to 26 months of age was studied. The three major brain areas, the forebrain, cerebellum, and the brain stem, were studied separately. The concentration of the esters in each brain region was the highest at the earliest fetal age of 13 weeks and fell during growth. However, transient rises in the concentration were observed, at about birth in the forebrain and at 4–5 months after birth in the cerebellum The peak concentration during the transient period (125–150 μg/g fresh tissue of forebrain and 100–125 μg/g of cerebellum) was similar to the concentrations observed in the two parts respectively during early fetal ages. The brain stem also showed similar transient peak at about a few weeks before birth, but only when the esters were expressed as amount per cell. In absolute terms, a clear transient period was evident in the forebrain between birth and 9 months, while in the cerebellum or the brain stem, the total amount of the esters increased up to about 1 year of age and then remained almost unchanged. The major fatty acids of the esters were palmitic, palmitoleic, stearic, oleic, linoleic and arachidonic acid. Most of these fatty acids showed certain changes in relative proportions during development. Thus, in the forebrain, palmitic and oleic acid decreased from about 32% and 40% (weight percentages) at 13–15 weeks of gestation to about 20% and 25% respectively at 26 months of age. During this period, linoleic and arachidonic acid increased from about 3% and S% to about 10% and 24%, respectively. Most of these changes occurred after birth. The cerebellum and the brain stem differed only slightly from the forebrain in either the fatty acid composition or the pattern of the developmental changes in the composition.     

Modification of yeast ribosomal proteins. Phosphorylation.

Two-dimensional polyacrylamide-gel electrophoretic analysis of yeast ribosomal proteins labelled in vivo with 32PO43- revealed that the proteins S2 and S10 of the 40S ribosomal subunit, and the proteins L9, L30, L44 and L45 of the 60S ribosomal subunit, are phosphorylated in vivo. Most of the phosphate groups appeared to be linked to serine residues. Teh number of phosphate groups per molecule of phosphorylated protein species ranged from 0.01 to 0.79. Since most of the phosphorylated ribosomal proteins appear to associate with the pre-ribosomal particles at a very late stage of ribosome assembly, phosphorylation is more likely to play a role in the functioning of the ribosome than in its assembly.