Evolution of Orthologous Intronless and Intron-Bearing Globin Genes in Two Insect Species

While globin genes ctt-2β and ctt-9.1 in Chironomus thummi thummi each have a single intron, all of the other insect globin genes reported so far are intronless. We analyzed four globin genes linked to the two intron-bearing genes in C. th. thummi. Three have a single intron at the same position as ctt-2β and ctt-9.1; the fourth is intronless and lies between intron bearing genes. Finally, in addition to its intron, one gene (ctt-13RT) was recently interrupted by retrotransposition. Phylogenetic analyses show that the six genes in C. th. thummi share common ancestry with five globin genes in the distantly related species C. tentans, and that a 5-gene ancestral cluster predates the divergence of the two species. One gene in the ancestral cluster gave rise to ctn-ORFB in C. tentans, and duplicated in C. th. thummi to create ctt-11 and ctt-12. From parsimonious calculations of evolutionary distances since speciation, ctt-11, ctt-12, and ctn-ORFB evolved rapidly, while ctn-ORFE in C. tentans evolved slowly compared to other globin genes in the clusters. While these four globins are under selective pressure, we suggest that most chironomid globin genes were not selected for their unique function. Instead, we propose that high gene copy number itself was selected because conditions favored organisms that could synthesize more hemoglobin. High gene copy number selection to produce more of a useful product may be the basis of forming multigene families, all of whose members initially accumulate neutral substitutions while retaining essential function. Maintenance of a large family of globin genes not only ensured high levels of hemoglobin production, but may have facilitated the extensive divergence of chironomids into as many as 5000 species. Received: 31 December 1996 / Accepted: 16 May 1997     

Effects of Surface Plasmon Coupling on the Whispering-Gallery Resonance in a Hexagonal Nanowire Cavity Structure

Plasmonics - The effects of surface plasmon (SP) coupling with the excitation radiating dipole on the behaviors of the whispering-gallery resonance (WGR) modes in a hexagonal GaN nanowire cavity...     

The zinc ion in the HNH motif of the endonuclease domain of colicin E7 is not required for DNA binding but is essential for DNA hydrolysis

The HNH motif was originally identified in the subfamily of HNH homing endonucleases, which initiate the process of the insertion of mobile genetic elements into specific sites. Several bacteria toxins, including colicin E7 (ColE7), also contain the 30 amino acid HNH motif in their nuclease domains. In this work, we found that the nuclease domain of ColE7 (nuclease-ColE7) purified from Escherichia coli contains a one-to-one stoichiometry of zinc ion and that this zinc-containing enzyme hydrolyzes DNA without externally added divalent metal ions. The apo-enzyme, in which the indigenous zinc ion was removed from nuclease-ColE7, had no DNase activity. Several divalent metal ions, including Ni²⁺, Mg²⁺, Co²⁺, Mn²⁺, Ca²⁺, Sr²⁺, Cu²⁺ and Zn²⁺, re-activated the DNase activity of the apo-enzyme to various degrees, however higher concentrations of zinc ion inhibited this DNase activity. Two charged residues located at positions close to the zinc-binding site were mutated to alanine. The single-site mutants, R538A and E542A, showed reduced DNase activity, whereas the double-point mutant, R538A + E542A, had no observable DNase activity. A gel retardation assay further demonstrated that the nuclease-ColE7 hydrolyzed DNA in the presence of zinc ions, but only bound to DNA in the absence of zinc ions. These results demonstrate that the zinc ion in the HNH motif of nuclease-ColE7 is not required for DNA binding, but is essential for DNA hydrolysis, suggesting that the zinc ion not only stabilizes the folding of the enzyme, but is also likely to be involved in DNA hydrolysis.     

Chromatic cues to trap the oriental fruit fly, Bactrocera dorsalis

Various colors have been used as visual cues to trap insect pests. For example, yellow traps for monitoring and control of the oriental fruit fly (Bactrocera dorsalis) have been in use for a very long time. However, the chromatic cue of using color traps has never been meticulously investigated. In this study, the spectral sensitivities of the photoreceptors in the compound eyes of B. dorsalis were measured intracellularly, and the theory of receptor quantum catch was applied to study the chromatic cue of fly attracting. Responses to five wavelength categories with peak wavelengths of 370, 380, 490, and 510 nm, and one with dual peaks at 350 and 490 nm were recorded. Based on spectral sensitivities, six colored papers were chosen to test the color preference of the fly, and an additional UV preference test was done to confirm the effect of the UV stimuli. It was concluded that UV and green stimuli (spectra: 300-380 nm and 500-570 nm) would enhance the attractiveness of a colored paper to the oriental fruit fly, and blue stimuli (380-500 nm) would diminish the attractiveness.     

Action spectra of phototactic responses of the flea beetle, Phyllotreta striolata

Abstract.  Adult flea beetles, Phyllotreta striolata , show a strong positive phototactic response. The action spectrum of phototaxis of dark-adapted beetles was measured with minimal required light intensity between the wavelength range of 300 nm and 600 nm. Male and female flea beetles showed identical phototacitc behaviours. The beetles were most sensitive to light with peak wavelengths between 350 nm and 430 nm in the morning. In the afternoon and evening, the sensitivity to wavelengths shorter than 430 nm decreased, but they remained most sensitive to 430 nm. These results suggest that changes in sensitivity of the photoreceptors or nervous integration influence the phototactic responses, and that the blue wavelengths are more attractive than others.     

Enhancement of Emission Efficiency of Deep-Ultraviolet AlGaN Quantum Wells Through Surface Plasmon Coupling with an Al Nanograting Structure

The enhancement of the internal quantum efficiency (IQE) of deep-ultraviolet Al _x Ga_1-x N/Al _y Ga_1-y N (x < y) quantum wells (QWs) by fabricating one-dimensional Al nanogratings on a QW structure for inducing surface plasmon (SP) coupling is demonstrated. Through temperature-dependent photoluminescence (PL) measurement, the enhancements of IQE in different emission polarizations are illustrated. Due to the small difference in energy band level between the heavy/light hole and split-off valence bands, the IQEs of the transverse electric- (TE-) and transverse magnetic- (TM-) polarized emissions are about the same. When emission polarization is perpendicular to Al-grating ridges, the SP resonance mode for coupling with the QWs is dominated by localized surface plasmon (LSP). When emission polarization is parallel with Al-grating ridges, the coupled SP resonance mode may mix LSP and SP polariton. In this polarization, LSP can be excited because of the width fluctuation of a grating ridge. When the excitation laser polarization is perpendicular to Al-grating ridges, the strong LSP resonance at the excitation laser wavelength leads to stronger excitation and hence higher IQE levels.     

Sequence and evolution of the gene for the monomeric globin I and its linkage to genes coding for dimeric globins in the insect Chironomus thummi

We isolated genomic clones containing sequences encoding globins I and IA from a Chironomus thummi thummi genomic library. Three clones contain globin IA (ctt-1A) genes, while one contains a globin I (ctt-1) gene. The coding regions of the four genes are identical except for the single base substitution accounting for the globin I/IA polymorphism. The noncoding DNA flanking the coding region is more than 98% similar, confirming a previous hypothesis that the globin ctt-1 and ctt-1A genes are alleles. Hemoglobins I and IA are monomeric in the insect hemolymph. Earlier in situ hybridization studies suggested that monomeric and dimeric globin genes are clustered at different chromosomal loci. In situ hybridization of ctt-1 DNA to polytene salivary gland chromosomes places the ctt-1 gene on the same band as genes for the dimeric globins II and VIIB, forcing revision of the earlier hypothesis that genes for monomeric and dimeric globin genes are at different loci. The evolution of the ctt-1 and ctt-1A alleles and of the two globin gene loci are discussed. Correspondence to: G. Bergtrom     

Individual variations in the content of giant secretory polypeptides in salivary glands of Chironomus

Salivary glands in aquatic larvae of Chironomus are responsible for formation of a fiber that larvae use to construct feeding tubes. Major constituents of this fiber include a family (the sp-I family) of high M _r (1 × 10⁶) secretory polypeptides. Because of our interest in the polypeptide composition and polymerization of the salivary fiber we conducted a survey of the electrophoretic pattern of sp-I components found in salivary glands obtained from individual larvae. The survey encompassed ten strains of Chironomus tentans, three strains of Chironomus pallidivittatus and four strains of Chironomus thummi. Salivary glands from C. tentans and C. pallidivittatus contained at least four sp-I components (sp-Ia, sp-Ib, sp-Ic and sp-Id) that behave identically with regard to their electrophoretic mobility and detectability when larvae were exposed to galactose or glycerol. Sp-I components in C. thummi were generally fewer and not directly comparable by electrophoretic mobility to sp-I components in the other two species. During this survey two important alterations were observed in the electrophoretic pattern of sp-I components obtained from C. tentans and C. pallidivittatus. First, all four sp-I components exhibited, with a low frequency, double bands that appeared as slow-versus-fast electrophoretic variants of a particular component. Secondly, the relative steady-state level of each sp-I component fluctuated in comparison to other sp-I components in the same extract. This fluctuation varied such that any one sp-I component might appear as a single prominent component. Sp-I components are encoded by a multigene family located in Balbiani rings (BRs). Results presented here, in conjunction with known nucleotide sequence data from BR genes, led us to the following conclusions. The slow and fast electrophoretic variants observed for each sp-I component suggest that each corresponding BR gene may be able to expand and/or contract in size. The observed degree of independent fluctuation in the steady-state level of each sp-I component suggests that each BR gene may be able to regulate its expression independently from the others. Finally, the observation that salivary glands sometimes contained only one prominent sp-I component led us to hypothesize that, whereas salivary fibers might typically be heteropolymers comprised of two or more types of sp-I components, homopolymers comprised of only one sp-I component may also exist.     

Identification and characterization of H10 enzymes isolated from <Emphasis Type="Italic">Bacillus</Emphasis><Emphasis Type="Italic">cereus</Emphasis> H10 with keratinolytic and proteolytic activities

Two types of extracellular proteases with molecular mass of 50.0 and 44.8 kDa were found in H10 enzymes partially purified from Bacillus cereus H10. Further identification using liquid chromatography-tandem mass spectrometry, the enzyme with 50.0 kDa was identified as being similar to leucine dehydrogenase; while the enzyme with 44.8 kDa might be a novel keratinolytic enzyme with little similarity to other proteins. To maximize the keratinolytic and proteolytic abilities in the H10 enzymes, a combination of response surface methodology and sequential quadratic programming technique was used to study the hydrolytic pH and temperature. Results showed that the H10 enzymes could produce optimal proteolytic and keratinolytic activities at a hydrolysis temperature of 59°C at pH 7.57. Testing the protease activity on various protein substrates and temperatures indicated that the H10 enzymes showed high thermal stability and were very effective in porcine hair.