Pre‐copulation intervals,copulation frequencies,and initial progeny sex ratios in two biotypes of whitefly,Bemisia tabaci

The whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is a species complex, and its systematic classification requires controlled crossing experiments among its genetic groups. Accurate information on pre‐copulation intervals, copulation frequencies, and initial frequency of egg fertilization of newly emerged adults is critical for designing procedures for collecting the virgin adults necessary for these experiments. In the literature, considerable variation is reported between B. tabaci populations, with respect to the length of the pre‐copulation interval and the initial frequency of egg fertilization. Here, we used a video‐recording method to observe continuously the copulation behaviour of the Mediterranean/Asia Minor/Africa (B biotype) and the Asia II (ZHJ1 biotype) groups of B. tabaci. We also recorded the initial frequency of egg fertilization, as determined by the sex of the progeny. When adults were caged in female–male pairs on leaves of cotton plants, the earliest copulation events occurred 2–6 h after emergence; at 12 h after emergence 56–84% of the females had copulated at least once, and nearly all (92–100%) had copulated at least once by 36 h after emergence. Both females and males copulated repeatedly. Approximately 80 and 20% of copulation events occurred during the photophase and scotophase, respectively. By 72 h post‐emergence, the females of the B and ZHJ1 biotypes had copulated on average 6.1 and 3.9 times, respectively. When adults were caged in groups on plants 1–13 h after emergence, 30–35% of the eggs deposited during this period were fertilized, and approximately 90% of females were fertilized by the end of the 13 h. Although timing of copulation differed in detail between the two genetic groups, the results demonstrate that B. tabaci adults can start to copulate as early as 2–6 h post‐emergence and the majority of females can become fertilized on the day that they emerge.     

Attachment as a factor in the protection of Enterobacter cloacae from chlorination

Enterobacter cloacae attached to drinking water distribution particles was subjected to chlorination. Attachment resulted in the protection of these organisms from disinfection. This effect was found to be dependent upon both the level of chlorine in the system and attachment time. The results obtained in this study indicate that attached organisms may play an important role in coliform outbreaks.     

cDNA and protein sequence of a major pea seed albumin (PA 2 : Mr≈26 000)

Summary Pea albumin 2 (PA2:M_r26000) is a major component of the albumin fraction derived from aqueous salt extracts of pea seed. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and chromatography on DEAE-Sephacel resolve PA2 into two closely related components (PA2a and PA2b). A cDNA clone coding for one of these components has been sequenced and the deduced amino acid sequence compared with partial, chemically-determined sequences for cyanogen bromide peptides from both PA2 components. Complete amino acid sequences were obtained for the C-terminal peptides. The PA2 molecule of 230 amino acids contains four imperfect repeat sequences each of approximately 57 amino acids in length.The combined sequence data, together with a comparison of PA2-related polypeptides produced in vitro and in vivo, indicate that PA2 is synthesized without a signal sequence and does not undergo significant post-translational modification. Although both forms of PA2 contain Asn-X-Thr consensus sequences, neither form is glycosylated. Accumulation of PA2 contributes approximately 11% of the sulfur-amino acids in pea seeds (cysteine plus methionine equals 2.6 residues percent). Suppression of levels of PA2 polypeptides and their mRNAs in developing seeds of sulfur-deficient plants is less marked than that for legumin, in spite of the lower content of sulfur-amino acids in legumin.     

Antigenic structure and variation in an influenza virus N9 neuraminidase.

We previously determined, by X-ray crystallography, the three-dimensional structure of a complex between influenza virus N9 neuraminidase (NA) and the Fab fragments of monoclonal antibody NC-41 [P. M. Colman, W. G. Laver, J. N. Varghese, A. T. Baker, P. A. Tulloch, G. M. Air, and R. G. Webster, Nature (London) 326:358-363, 1987]. This antibody binds to an epitope on the upper surface of the NA which is made up of four polypeptide loops over an area of approximately 600 A2 (60 nm2). We now describe properties of NC-41 and other monoclonal antibodies to N9 NA and the properties of variants selected with these antibodies (escape mutants). All except one of the escape mutants had single amino acid sequence changes which affected the binding of NC-41 and which therefore are located within the NC-41 epitope. The other one had a change outside the epitope which did not affect the binding of any of the other antibodies. All the antibodies which selected variants inhibited enzyme activity with fetuin (molecular weight, 50,000) as the substrate, but only five, including NC-41, also inhibited enzyme activity with the small substrate N-acetylneuramin-lactose (molecular weight, 600). These five probably inhibited enzyme activity by distorting the catalytic site of the NA. Isolated, intact N9 NA molecules form rosettes in the absence of detergent, and these possess high levels of hemagglutinin activity (W.G. Laver, P.M. Colman, R.G. Webster, V.S. Hinshaw, and G.M. Air, Virology 137:314-323, 1984). The enzyme activity of N9 NA was inhibited efficiently by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, whereas hemagglutinin activity was unaffected. The NAs of several variants with sequence changes in the NC-41 epitope lost hemagglutinin activity without any loss of enzyme activity, suggesting that the two activities are associated with separate sites on the N9 NA head.     

Sequence and translation of the murine coronavirus 5''-end genomic RNA reveals the N-terminal structure of the putative RNA polymerase.

A 28-kilodalton protein has been suggested to be the amino-terminal protein cleavage product of the putative coronavirus RNA polymerase (gene A) (M.R. Denison and S. Perlman, Virology 157:565-568, 1987). To elucidate the structure and mechanism of synthesis of this protein, the nucleotide sequence of the 5' 2.0 kilobases of the coronavirus mouse hepatitis virus strain JHM genome was determined. This sequence contains a single, long open reading frame and predicts a highly basic amino-terminal region. Cell-free translation of RNAs transcribed in vitro from DNAs containing gene A sequences in pT7 vectors yielded proteins initiated from the 5'-most optimal initiation codon at position 215 from the 5' end of the genome. The sequence preceding this initiation codon predicts the presence of a stable hairpin loop structure. The presence of an RNA secondary structure at the 5' end of the RNA genome is supported by the observation that gene A sequences were more efficiently translated in vitro when upstream noncoding sequences were removed. By comparing the translation products of virion genomic RNA and in vitro transcribed RNAs, we established that our clones encompassing the 5'-end mouse hepatitis virus genomic RNA encode the 28-kilodalton N-terminal cleavage product of the gene A protein. Possible cleavage sites for this protein are proposed.     

Relationships among pure cultured strains of Frankia based on host specificity

Fifty strains of Frankia were tested for their ability to nodulate six species of actinorhizal plants. Pure cultured strains were used to inoculate seedlings of Alnus glutinosa (L.) Gaertn., Alnus rubra Bong., Casuarina equisetifolia L., Elaeagnus angustifolia L., Hippophaë rhamnoides L. and Myrica cerifera L. in nutrient solution culture. From the results of this study, host inoculation groups among the actinorhizal plants were defined. Although overlap between host inoculation groups appears to be common, the results from this study did not support the view that Frankia strains are promiscuous. All Frankia strains tested in this study could easily be classified into four major host-specificity groups.     

Transport and Compartmentation of 1-Aminocyclopropane-1-Carboxylic Acid and Its Structural Analog, alpha-Aminoisobutyric Acid, in Tomato Pericarp Slices

The uptakes of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor to ethylene, and its structural analog, α-aminoisobutyric acid (αAIB) by tomato pericarp slices were investigated. Both uptakes show a biphasic (saturable-linear) dependence on external concentration of the transported amino acid. At low concentrations, ACC uptake is competitively inhibited by αAIB and vice versa. Both uptakes also are inhibited by other neutral amino acids but not by acidic or basic amino acids. ACC and αAIB uptakes are metabolically dependent and are increased with time of tissue incubation. αAIB efflux patterns from pericarp slices indicated three distinct αAIB compartments having efflux kinetics consistent with those for cell wall, cytoplasm, and vacuole. The bulk of the αAIB taken up by pericarp tissue is sequestered into the vacuole. The ability of pericarp tissue to accumulate αAIB in the vacuole declines with fruit development.     

Release of a chimeric protein into the medium from Escherichia coli using the C-terminal secretion signal of haemolysin.

Recently, we have identified a novel topogenic sequence at the C terminus of Escherichia coli haemolysin (HlyA) which is essential for its efficient secretion into the medium. This discovery has introduced the possibility of using this secretion system for the release of chimeric proteins from E. coli directly into the medium. We have now successfully fused this C-terminal signal to a hybrid protein containing a few residues of beta-galactosidase and the majority of the E. coli outer membrane porin OmpF lacking its own N-terminal signal sequence. We find that this chimeric protein is specifically translocated across the inner and outer membranes and is released into the medium. In addition, we have further localized the HlyA secretion signal to the final 113 amino acids of the C terminus. In fact, a specific secretion signal appears to reside at least in part within the last 27 amino acids of HlyA.     

Cartilage proteoglycan aggregates. The link protein and proteoglycan amino-terminal globular domains have similar structures

Cartilage proteoglycan aggregates contain two components (proteoglycan monomer and link protein) which interact with each other and with hyaluronic acid. Data from amino acid sequence analysis are presented that shows that a domain of the proteoglycan, the hyaluronic acid binding region, which interacts with link protein and hyaluronic acid is very similar to link protein in terms of its primary structure. However, the pattern of glycosylation in the hyaluronic acid binding region is different from that found in link protein. After removal of N-linked oligosaccharides, the tryptically prepared hyaluronic acid binding region from rat chondrosarcoma has a mass by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of 43 +/- 2 kDa. The COOH-terminal two-thirds of rat chondrosarcoma link protein, starting at residue 105, has 41.3% identity with a similar region in the hyaluronic acid binding region. We show that, in addition to the hyaluronic acid binding region, proteoglycan contains another region with similarity to the two repeating loop structures in the COOH-terminal two-thirds of link protein. This presumably corresponds to the second globular domain reported in rotary shadowing studies of cartilage proteoglycans. We have deduced the positions of all of the disulfide bonds in the hyaluronic acid binding region and find them to be in the same positions as would be expected from comparison of these sequences with link protein.