First detection of viruses in africanized honey bees from Peru

<正>Dear Editor,The ability of the Western honey bee,Apis mellifera,to adapt to most climates of the world and the ongoing standardization of colony management has made this species of honey bees the most important species for crop pollination.In recent years,Peru emerged as a main exporter of industrial crops.This industry is mainly concentrated in the Peruvian coastal region,because the local climate permits off-season production     

Comparative analysis of the virulence control systems of Bordetella pertussis and Bordetella bronchiseptica

Bordetella pertussis and Bordetella bronchiseptica contain nearly identical BvgAS signal-transduction systems that mediate a biphasic transition between virulent (Bvg⁺) and avirulent (Bvg^–) phases. In the Bvg⁺ phase, the two species express a similar set of adhesins and toxins, and in both organisms the transition to the Bvg^– phase occurs in response to the same environmental signals (low temperature or the presence of nicotinic acid or sulphate anion). These two species differ, however, with regard to Bvg^–-phase phenotypes, host specificity, the severity and course of the diseases they cause, and also potentially in their routes of transmission. To investigate the contribution of the virulence-control system to these phenotypic differences, we constructed a chimeric B. bronchiseptica strain containing bvgAS from B. pertussis and compared it with wild-type B. bronchiseptica in vitro and in vivo . The chimeric strain was indistinguishable from the wild type in its ability to express Bvg⁺- and Bvg^–-phase-specific factors. However, although the chimeric strain responded to the same signals as the wild type, it differed dramatically in sensitivity to these signals; significantly more nicotinic acid or MgSO₄ was required to modulate the chimeric strain compared with the wild-type strain. Despite this difference in signal sensitivity, the chimeric strain was indistinguishable from the wild type in its ability to cause respiratory-tract infections in rats, indicating that the bvgAS loci of B. pertussis and B. bronchiseptica are functionally interchangeable in vivo . By exchanging discrete fragments of bvgAS , we found that the periplasmic region of BvgS determines signal sensitivity.     

Determinants of the DNA-binding specificity of the Avian homeodomain protein, AKR.

AKR (Avian Knotted-Related) was the first example of a vertebrate homeodomain protein with a highly divergent Ile residue at position 50 of the DNA-recognition helix. The protein was cloned from a liver cDNA expression library of a day-9 chick embryo by virtue of its ability to bind to the F' site in the proximal promoter of the avian apoVLDLII gene. Expression of the apoVLDLII gene is completely estrogen dependent, and mutation or deletion of the F' site decreases estrogen inducibility 5- to 10-fold. Subsequent data indicated that AKR is capable of repressing the hormone responsiveness of the apoVLDLII promoter, specifically through binding to F'. Involvement of the F' site in the hormone-dependent activation of apoVLDLII gene expression, as well as AKR-mediated repression, strongly suggests that both positive and negative regulatory factors interact with this site. Although several mammalian proteins have now been isolated whose homeodomains share many of the structural features of AKR, including the Ile at position 50, little is known of their functions in vivo or the identities of the genes they regulate. Consequently, the elements through which they exert their effects and the structural determinants of their binding specificities remain largely uncharacterized. In this study, we defined the sequence specificity of binding by AKR using polymerase chain reaction-assisted optimal site selection and determined the affinity with which the protein binds to both the optimized site and the F' site. Additionally, we generated a three-dimensional model of the AKR homeodomain binding to its optimized site and probed the validity of the model by examining the consequences of mutating amino acid residues in recognition helix 3 and the N-terminal arm on the binding specificity of the homeodomain. Finally, we present evidence that the F' site itself may act as an estrogen response element (ERE) when in the vicinity of imperfect or canonical EREs and that AKR can repress hormone inducibility mediated via this site.