We report here the breakpoint structure and sequences of the Drosophila melanogaster cosmopolitan chromosomal inversion In(3R)P. Combining in situ hybridization to polytene chromosomes and long-range PCR, we have identified and sequenced the distal and proximal breakpoints. The breakpoints are not simple cutand-paste structures; gene fragments and small duplications of DNA are associated with both breaks. The distal breakpoint breaks the tolkin (tok) gene and the proximal breakpoint breaks CG31279 and the tolloid (tld ) gene. Functional copies of all three genes are found at the opposite breakpoints. We sequenced a representative sample of standard (St ) and In(3R)P karyotypes for a 2-kb portion of the tok gene, as well as the same 2 kb from the pseudogene tok fragment found at the distal breakpoint of In(3R)P chromosomes. The tok gene in St arrangements possesses levels of polymorphism typical of D. melanogaster genes. The functional tok gene associated with In(3R)P shows little polymorphism. Numerous single-base changes, as well as deletions and duplications, are associated with the truncated copy of tok. The overall pattern of polymorphism is consistent with a recent origin of In(3R)P, on the order of N e generations. The identification of these breakpoint sequences permits a simple PCR-based screen for In(3R)P. 1996). sophila pseudoobscura, chromosome inversions claim an important place in the early study of genetic variation However, topological constraint on homolog pairing increases with increasing proximity to the inversion breakin natural populations (Powell 1997). Because inversions reduce recombination in heterokaryotypes, they points (Novitski and Braver 1954). This increase in constraint results in decreasing crossing over with inare a genomic feature with potential to come under natural selection and play a role in evolution. A common creasing proximity to the breakpoints. For this reason, recovering nucleotide sequences as close to the breakbelief is that inversion polymorphisms are maintained by balancing selection (Dobzhansky 1970). If so, indipoints as possible offers the most informative way to study the population genetics of inversion polymorphisms. vidual inversions might be ancient, that is, old relative to a hypothetical neutral arrangement (Andolfatto Finally, the structural features at the breakpoints may also offer insight into the molecular nature and mutational et al. 2001). This age hypothesis can be examined by comparing patterns and levels of sequence variation origin of the inversion (e.g., transposable elements), the potential for genetic damage by disrupting gene function, between and within inverted and standard (St) arrangements. Inverted regions are subject to reduced recombiand the genealogical uniqueness of the arrangement. Drosophila melanogaster possesses well-studied cosmonation. On a timescale relevant to the question of balancing selection, however, recombination is often not politan inversion polymorphisms on all four autosomal arms, as well as a common X-lin...

In this report, we use synthetic, activity-variant alleles in Drosophila melanogaster to quantify interactions across the enzyme network that reduces nicotinamide adenine dinucleotide phosphate (NADP) to NADPH. We examine the effects of large-scale variation in isocitrate dehydrogenase (IDH) or glucose-6-phosphate dehydrogenase (G6PD) activity in a single genetic background and of smaller-scale variation in IDH, G6PD, and malic enzyme across 10 different genetic backgrounds. We find significant interactions among all three enzymes in adults; changes in the activity of any one source of a reduced cofactor generally result in changes in the other two, although the magnitude and directionality of change differs depending on the gene and the genetic background. Observed interactions are presumably through cellular mechanisms that maintain a homeostatic balance of NADPH/NADP, and the magnitude of change in response to modification of one source of reduced cofactor likely reflects the relative contribution of that enzyme to the cofactor pool. Our results suggest that malic enzyme makes the largest single contribution to the NADPH pool, consistent with the results from earlier experiments in larval D. melanogaster using naturally occurring alleles. The interactions between all three enzymes indicate functional interdependence and underscore the importance of examining enzymes as components of a network.

An important question in evolutionary and physiological genetics is how the control of flux-base phenotypes is distributed across the enzymes in a pathway. This control is often related to enzymespecific levels of activity that are reported to be in excess of that required for demand. In glycolysis, metabolic control is frequently considered vested in classical regulatory enzymes, each strongly displaced from equilibrium. Yet the contribution of individual steps to control is unclear. To assess enzyme-specific control in the glycolytic pathway, we used P-element excision-derived mutagenesis in Drosophila melanogaster to generate full and partial knockouts of seven metabolic genes and to measure tethered flight performance. For most enzymes, we find that reduction to half of the normal activity has no measurable impact on wing beat frequency. The enzymes catalyzing near-equilibrium reactions, phosphoglucose isomerase, phosphoglucomutase, and triosephosphate isomerase fail to show any decline in flight performance even when activity levels are reduced to 17% or less. At reduced activities, the classic regulatory enzymes, hexokinase and glycogen phosphorylase, show significant drops in flight performance and are nearer to saturation. Our results show that flight performance is canalized or robust to the activity variation found in natural populations. Furthermore, enzymes catalyzing near-equilibrium reactions show strong genetic dominance down to low levels of activity. This implies considerable excess enzyme capacity for these enzymes.I dentifying the causes of the differing patterns of molecular evolution among genes is a compelling problem in biology. In Drosophila and yeast, genome-wide studies have emphasized gene-specific variables, such as codon bias, expression level, dispensability, and connectedness, to establish correlations with the levels of purifying selection (1-7). One complex but unexplored cause of variation is the relative difference among enzymes that functional variation imparts to phenotype. When the phenotypic variation reflects the flux rate through a pathway, this relationship between enzyme activity and phenotype is defined by the level of flux control. For enzyme steps with little flux control, activity differences will have no impact on phenotypic variation and will have consequently no effect on phenotype-associated fitness. For this reason, the relative level of control at an enzyme step is expected to be a predictor of molecular evolution for a gene. The goal of this study is to evaluate the control of flight performance associated with activity variation for a number of enzymes of the glycolytic pathway.Flux control is expected to differ among enzymes as a result of pathway context, equilibrium status, and the presence or absence of steady-state conditions (8). The classical view of metabolic flux control proposes that unique steps, such as those under allosteric control and strongly displaced from equilibrium, control the pathway flux. These steps represent the textbook regulatory e...

We have created a set of P-element excision-derived Gpdh alleles that generate a range of GPDH activity phenotypes ranging from zero to full activity. By placing these synthetic alleles in isogenic backgrounds, we characterize the effects of minor and major activity variation on two different aspects of Gpdh function: the standing triglyceride pool and glycerol-3-phosphate shuttle-assisted flight. We observe small but statistically significant reductions in triglyceride content for adult Gpdh genotypes possessing 33-80% reductions from normal activity. These small differences scale to a notable proportion of the observed genetic variation in triglyceride content in natural populations. Using a tethered fly assay to assess flight metabolism, we observed that genotypes with 100 and 66% activity exhibited no significant difference in wingbeat frequency (WBF), while activity reductions from 60 to 10% showed statistically significant reductions of 7% in WBF. These studies show that the molecular polymorphism associated with GPDH activity could be maintained in natural populations by selection in the triglyceride pool.

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We have isolated and characterized cDNAs representing two distinct pheromone binding proteins (PBPs) from the gypsy moth, Lymantria dispar. We use the L. dispar protein sequences, along with other published lepidopteran PBPs, to investigate the evolutionary relationships among genes within the PBP multigene family. Our analyses suggest that the presence of two distinct PBPs in genera representing separate moth superfamilies is the result of relatively recent, independent, gene duplication events rather than a single, ancient, duplication. We discuss this result with respect to the biochemical diversification of moth PBPs.