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Transposons have had a pivotal role in genome evolution.sup.1 and are believed to be the evolutionary progenitors of the RAG1-RAG2 recombinase.sup.2, an essential component of the adaptive immune system in jawed vertebrates.sup.3. Here we report one crystal structure and five cryo-electron microscopy structures of Transib.sup.4,5, a RAG1-like transposase from Helicoverpa zea, that capture the entire transposition process from the apo enzyme to the terminal strand transfer complex with transposon ends covalently joined to target DNA, at resolutions of 3.0-4.6 Å. These structures reveal a butterfly-shaped complex that undergoes two cycles of marked conformational changes in which the 'wings' of the transposase unfurl to bind substrate DNA, close to execute cleavage, open to release the flanking DNA and close again to capture and attack target DNA. Transib possesses unique structural elements that compensate for the absence of a RAG2 partner, including a loop that interacts with the transposition target site and an accordion-like C-terminal tail that elongates and contracts to help to control the opening and closing of the enzyme and assembly of the active site. Our findings reveal the detailed reaction pathway of a eukaryotic cut-and-paste transposase and illuminate some of the earliest steps in the evolution of the RAG recombinase. Analysis of multiple structures of the Helicoverpa zea DNA transposase Transib, determined by X-ray crystallography and cryo-electron microscopy, reveals the detailed pathway of the transposition reaction and sheds light on the evolution of the RAG recombinase., Author(s): Chang Liu [sup.1] , Yang Yang [sup.2] [sup.3] , David G. Schatz [sup.1] Author Affiliations: (1) Department of Immunobiology, Yale School of Medicine, New Haven, USA (2) Department of [...]

C-glycosyl flavones in maize silks confer resistance (i.e., antibiosis) to corn earworm (Helicoverpa zea [Boddie]) larvae and are distinguished by their B-ring substitutions, with maysin and apimaysin being the di- and monohydroxy B-ring forms, respectively. Herein, we examine the genetic mechanisms underling the synthesis of maysin and apimaysin and the corresponding effects on corn earworm larval growth. Using an [F.sub.2] population, we found a quantitative trait locus (QTL), rem1, which accounted for 55.3% of the phenotypic variance for maysin, and a QTL, pr1, which explained 64.7% of the phenotypic variance for apimaysin. The maysin QTL did not affect apimaysin synthesis, and the apimaysin QTL did not affect maysin synthesis, suggesting that the synthesis of these closely related compounds occurs independently. The two QTLs, rem1 and pr1, were involved in a significant epistatic interaction for total flavones, suggesting that a ceiling exists governing the total possible amount of C-glycosyl flavone. The maysin and apimaysin QTLs were significant QTLs for corn earworm antibiosis, accounting for 14.1% (rem1) and 14.7% (pr1) of the phenotypic variation. An additional QTL, represented by umc85 on the short arm of chromosome 6, affected antibiosis ([R.sup.2] = 15.2%), but did not affect the synthesis of the C-glycosyl flavones.

Comparison of European and African cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) populations for allozyme polymorphism at 15 loci for 22 populations is discussed. Few significant deviations from Hardy-Weinberg eqilibrium were seen other than at the Acp locus, and results are discussed as they relate to migratory abilities.

Moderately high and stable resistance to commercial Bt cotton varieties (Cry1Ac) toxin is attained in Helicoverpa zea and this resistance is characterized. The results have helped in understanding why the pest, cotton bollworm, has not evolved Bacillus thuringiensis resistance, and has highlighted the need to choose the form of Bacillus thuringiensis protein used in experiments.