Glucose 6-phosphate dehydrogenase inDrosophila melanogaster: Starch gel electrophoretic variation due to molecular instability

Two starch gel electrophoretic variants of glucose 6-phosphate dehydrogenase (G6PD) in Drosophila melanogasterwere partially purified and characterized biochemically. The difference in their migration on starch gel is not due to a charge difference, but rather to a difference in molecular size due to instability of one of the variants. Crosses between the two variants did not produce offspring showing an intermediate electrophoretic band in the heterozygous female. That an hybrid molecule does exist in the heterozygous female, however, was demonstrated by taking advantage of differences in heat lability and structural stability of the two variants. Hence, we conclude that the G6PD locus in both X-chromosomes is active in each cell in female Drosophila.Our findings with DrosophilaG6PD emphasize the importance to protein variation and enzyme function of mutations leading to amino acid substitutions which do not produce a change in net charge. Aided by National Institutes of Health grants HD 00486, HD 00004, and GM 14155.     

Source and Portal of Entry of Bacteria Found in Bruised Poultry Tissue

Bacteriological studies revealed that normal tissue, air sacs, feathers, skin of birds, poultry feed, gut, and chicken droppings were sources of the predominant organisms, including staphylococci, found in bruised poultry tissue. Further investigation of normal tissue revealed that after the intramuscular injection of Staphylococcus aureus, marker strain (MS), the organism was eliminated from these tissues within 7 days. However, when these tissues were traumatized 3 days after injection, the number of the test organism increased, and the organism was present on the 7th day after inoculation. Poultry feed and fecal material contained a large number of staphylococci identical to those isolated from bruised tissue (McCarthy, Brown, and Hamdy, 1963), thereby implicating the gut as a possible portal of entry. When a pathogenic marker strain of S. aureus was established in the intestinal tract of chickens by administering an active culture of this organism either in their drinking water or by gavage, it was recovered from the traumatized tissue. The incidence of positive culture of S. aureus MS in these tissues correlated with age of bruise, reaching 22 to 33% immediately after contusion and at the early stages of healing (1 to 3 days post bruise) and decreasing thereafter from 11 to 0% on the 4th through 6th days after bruise infliction. The air sac was also found to be a site by which bacteria may enter the traumatized tissues, but to a limited extent.     

Cloning, expression and sequence analysis of the SphI restriction-modification system

SphI, a type II restriction-modification (R-M) system from the bacterium Streptomyces phaeochromogenes, recognizes the sequence 5′-GCATGC. The SphI methyltransferase (MTase)-encoding gene, sphIM, was cloned into Escherichia coli using MTase selection to isolate the clone. However, none of these clones contained the restriction endonuclease (ENase) gene. Repeated attempts to clone the complete ENase gene along with sphIM in one step failed, presumably due to expression of SphI ENase gene, sphIR, in the presence of inadequate expression of sphIM. The complete sphIR was finally cloned using a two-step process. PCR was used to isolate the 3′ end of sphIR from a library. The intact sphIR, reconstructed under control of an inducible promoter, was introduced into an E. coli strain containing a plasmid with the NlaIII MTase-encoding gene (nlaIIIM). The nucleotide sequence of the SphI system was determined, analyzed and compared to previously sequenced R-M systems. The sequence was also examined for features which would help explain why sphIR unlike other actinomycete ENase genes seemed to be expressed in E. coli.     

竹红菌乙素对膜蛋白荧光猝灭研究

竹红菌乙素作为膜蛋白荧光猝灭剂,研究了乙素从水相进入膜体系过程中基本物理现象.包括了:膜与水分配系数(P);进入速度;以及膜与水相的体积比(α),并对其猝灭机理进行深入探讨.结果表明,乙素对膜蛋白质荧光的猝灭服从动态猝灭原理;用ESR技术直接观察到:激发态的色氨酸可以将电子转移给乙素并形成乙素自由基,因此用电子转移方程:K_et=K₀exp(-R)处理猝灭反应过程中的K_q值,可以方便地得到Trp-HB分子间距离(R)信息.     

RAPID LABORATORY EVOLUTION OF ADULT LIFE-HISTORY TRAITS IN DROSOPHILA MELANOGASTER IN RESPONSE TO TEMPERATURE

Three replicate lines of Drosophila melanogaster were cultured at each of two temperatures (16.5°C and 25°C) in population cages for 4 yr. The lifespans of both sexes and the fecundity and fertility of the females were then measured at both experimental temperatures. The characters showed evidence of adaptation; flies of both sexes from each selection regime showed higher longevity, and females showed higher fecundity and fertility, than flies from the other selection regime when they were tested at the experimental temperature at which they had evolved. Calculation of intrinsic rates of increase under different assumptions about the rate of population increase showed that the difference between the lines from the two selection regimes became less the higher the rate of population increase, because the lines were more similar in early adulthood than they were later. Despite the increased adaptation of the low-temperature lines to the low temperature, like the high temperature lines they produced progeny at a higher rate at the higher temperature. The lines may have independently evolved adaptations to their respective thermal regimes during the experiment, or there may have been a trade-off between adaptation to the two temperatures, or mutation pressure may have lowered adaptation to the temperature that the flies no longer encountered.     

NATURAL SELECTION ON QUANTITATIVE TRAITS IN THE BOMBINA HYBRID ZONE

Observations on the means, variances, and covariances of quantitative traits across hybrid zones can give information similar to that from Mendelian markers. In addition, they can identify particular traits through which the cline is maintained. We describe a survey of six traits across the hybrid zone between Bombina bombina and Bombina variegata (Amphibia: Discoglossidae) near Pe??enica in Croatia. We obtained laboratory measuments of the belly pattern, skin thickness, mating call, skeletal form, egg size, and the developmental time of tadpoles. Although offspring from hybrid populations showed no evidence of reduced viability, a third of the F₁ families failed completely, irrespective of the direction of the cross. All traits differed significantly between the taxa. Clines in belly pattern, skin thickness, mating call, and skeletal form were closely concordant with clines in four diagnostic enzyme loci. However, the cline in developmental time was displaced towards bombina, and the cline in egg size was displaced towards variegata. This discordance could be because the traits are not inherited additively or because they are subject to different selection pressures. We favor the latter explanation in the case of developmental time. We show that moderate selection acting directly on a trait suffices to shift its position; rather stronger selection is needed to change its width appreciably. Within hybrid populations, there are significant associations among quantitative traits, and between traits and enzymes. Phenotypic variances also increase in hybrid populations. These observations can be explained by linkage disequilibria among the underlying loci. However, the average magnitude of the covariance between traits is about half that expected from the linkage disequilibria between enzyme loci. The discrepancy is not readily explained by nonadditive gene action. This puzzle is now unresolved and calls for further investigation.     

Natural attachment duration of nymphs of the tick Ixodes uriae (Acari: Ixodidae) on kittiwake Rissa tridactyla nestlings

Daily searches of the plumage of 62 kittiwake (Rissa tridactyla) chicks were carried out for 3 weeks to determine the attachment duration of the tick Ixodes uriae. All ticks recorded were nymphs and their mean duration of attachment was 5.2±1.7 days (n=93). Seventy-four per cent of the ticks survived to engorgement and were assumed to have fed successfully. The mean duration of attachment of successful ticks was 5.8±1.0 days (n=69), significantly longer than that of unsuccessful ticks (3.3±2.1 days, n=24). There was no difference in survival rates to engorgement between ticks attached to feathered and unfeathered parts of the body (78.3 and 79.2%, respectively), but the duration of attachment of successful ticks was significantly longer on unfeathered compared to feathered areas. There were no significant differences in the survival to engorgement or duration of attachment between ticks found on young (c.11 days) and old (>11 days) kittiwake nestlings. The attachment duration was not related to the total number of ticks found on the host or the number of ticks present in the immediate vicinity of the site of attachment. This work provides important data on the parameter of attachment durations of nymphal I. uriae on free-living kittiwakes; the data can be used for incorporation into the application of population modelling.     

A Membrane Receptor Mechanism for Steroid Hormones Reinitiating Meiosis in Xenopus Laevis Oocytes*

There is a membrane progesterone receptor in Xenopus laevis oocytes that undergo meiosis under steroid exposure. Early responses include a decrease of leucine uptake, a decrease of adenylate cyclase and alkaline phosphatase activities, and a decrease of the phosphorylation of a specific p48 protein in the membrane. These results are compatible with a decrease of membrane fluidity brought about by the hormonal message. However the above-cited effects as well as the Ca₂₊-changes are not yet enough well understood to be able to precisely delineate their role in meiosis reinitiation.     

GENETIC ANALYSIS OF A HYBRID ZONE BETWEEN THE FIRE-BELLIED TOADS,BOMBINA BOMBINA AND B. VARIEGATA,NEAR CRACOW IN SOUTHERN POLAND

The fire-bellied toads Bombina bombina and B. variegata differ extensively in biochemistry, morphology, and behavior. We use a survey of five diagnostic enzyme loci across the hybrid zone near Cracow in Southern Poland to estimate the dispersal rate, selection pressures, and numbers of loci which maintain this zone. The enzyme clines coincide closely with each other and with morphological and mitochondrial DNA clines. Although the zone lies on a broad transition between environments suitable for bombina and variegata, the close concordance of diverse characters, together with increased aberrations and mortality in hybrids, suggest that the zone is maintained largely by selection against hybrids. There are strong “linkage disequilibria” between each pair of (unlinked) enzyme loci (R? = 0.129 [2-unit support limits: 0.119–0.139]). These are probably caused by gene flow into the zone, and they give an estimate of dispersal (σ = 890 [790–940] m gen^?½). The clines are sharply stepped, with most of the change occurring within 6.15 (5.45–6.45) km, but with long tails of introgression on either side. This implies that the effective selection pressure on each enzyme marker (due largely to disequilibrium with other loci) is s* = 0.17 (0.159–0.181) at the center but that the selection acting directly on the enzyme loci is weak or zero (s_e < 0.0038). The stepped pattern implies a barrier to gene flow of 220 (48–415) km. This would substantially delay neutral introgression but would have little effect on advantageous alleles; the two taxa need not evolve independently. Strong selection is needed to maintain such a barrier: hybrid populations must have their mean fitness reduced by a factor of 0.65 (0.60–0.77). This selection must be spread over a large number of loci to account for the concordant patterns and the observed cline widths (N = 300 [80–2,000]).