How do mutations at phenylalanine-153 and isoleucine-155 partially suppress the effects of the aspartate-27-->serine mutation in Escherichia coli dihydrofolate reductase?

Several second-site suppressors of the D27S lesion in Escherichia coli dihydrofolate reductase (DHFR) have been identified. The activity of the primary mutant, D27S DHRF, was found to be greatly decreased at pH 7.0, consistent with aspartic acid-27 being critically involved in proton donation during catalysis. Partial suppressors of the D27S mutation have been selected by their ability to confer an increased resistance to trimethoprim upon host E. coli; the suppressors have been identified as F153S or I155N substitutions. D27S+F153S and D27S+I155N DHFRs display 2-3-fold increases in kcat over D27S DHFR values, but only the F153S mutation decreases the Km for dihydrofolate by a factor of 2. Neither double mutant approaches wild-type DHFR activity. Unexpectedly, Phe153 and Ile155 occur on the surface of the protein and are approximately 8 and 14 A distant from the active site. Ile155 is a member of a beta-bulge. A previously identified suppressing mutation, F137S, occurs nearby and is also a member of the same beta-bulge [Howell et al. (1990) Biochemistry 29, 8561-8569]. Clustering of these three second-site mutations indicates this area of the structure may be important in protein function. Conformational changes due to the presence of these suppressing mutations are likely as the F153S and I155N mutations do not affect hydride-transfer rates upon introduction in wild-type DHFR and alterations in circular dichroism spectra are associated with the double-mutant DHFRs.     

Identification of Host Fruit Volatiles from Flowering Dogwood (Cornus florida) Attractive to Dogwood-Origin Rhagoletis pomonella Flies

Solid-phase microextraction and gas chromatography coupled with electroantennographic detection were used to identify volatiles from fruit of flowering dogwood, Cornus florida, as key attractants for Rhagoletis pomonella flies originating from dogwood fruit. A six-component blend containing ethyl acetate (54.9%), 3-methylbutan-1-ol (27.5%), isoamyl acetate (0.9%), dimethyl trisulfide (1.9%), 1-octen-3-ol (9.1%), and -caryophyllene (5.8%) was identified from flowering dogwood fruit that gave consistent EAD activity. In a flight tunnel assay there was no significant difference in the response of individual dogwood flies exhibiting upwind anemotactic flight to volatile extracts from dogwood fruit and the six-component synthetic mixture. Dogwood flies also displayed significantly greater levels of upwind flight to sources with the dogwood volatile blend than with previously identified volatile blends from domestic apple or hawthorn fruit. Selected subtraction assays showed that the three-component mixture of 3-methylbutan-1-ol, 1-octen-3-ol, and -caryophyllene elicited levels of upwind flight to the source equivalent to the six-component mixture. Our study adds to previous ones showing that populations of Rhagoletis pomonella flies infesting apple, hawthorn, and flowering dogwood fruit are attracted to unique mixtures of fruit volatiles, supporting the hypothesis that host fruit odors could be key traits in sympatric host shifts and establishing host fidelity within members of the Rhagoletis pomonella species complex.     

Injection-seeded pulsed Ti:sapphire laser with novel stabilization scheme and capability of dual-wavelength operation

A gain-switched, single-frequency titanium-sapphire laser for atmospheric humidity measurements using the differential absorption lidar technique operating in the 820 nm wavelength region is described. The laser is pumped by a frequency-doubled, flashlamp-pumped Nd:YAG laser at a repetition rate of 50 Hz and injection seeded by two external-cavity-diode lasers. The system yields pulses with an energy of 15 mJ and high spectral purity. We describe a novel active injection-locking technique that avoids the problems of established methods like dither-lock or ramp-and-fire. Furthermore, our method opens the possibility to switch between two wavelengths for alternating shots, in contrast to most established techniques that only allow operation at one wavelength.     

Redundancy in a chemical signal: Behavioral responses of maleTrichoplusia ni to a 6-Component sex pheromone blend

The flight response of maleTrichoplusia ni was observed in a flight tunnel to a sex pheromone blend composed of six components:Z7–12Ac, 12Ac,Z5-12Ac, 11-12Ac,Z7-14Ac, and Z9-14Ac. The number of males reaching a 3000-g source of this blend was > 95%, equal to that observed to female glands and significantly greater than with the previously identified two-component blend (Z7-12Ac + 12Ac). In subtraction tests, all five-component blends, with the exception of the blend lacking the primary componentZ7-12Ac, and several four-component blends elicited similar peak levels of upwind flight, source contacts, and hairpencil displays to that observed with the six-component blend. We characterize the substitution of certain minor components for one another as a form of redundancy in the chemical signal and suggest that it contributes to response specificity and signal recognition in males. The results also support the concept that the full blend of components acts as a unit to influence male behavior at all phases of the response. Individual minor components were not responsible for eliciting specific behaviors in the sequence.     

Explicit expressions for geometrical dimensions of symmetrical coupled striplines

It is shown how the inverse solution of certain wave-impedance problems can be found explicitly by using Jacobi's theta functions. It is possible to find directly the geometrical dimensions, given the transmission-line wave-impedance parameters. Inverse formulas for a shielded single stripline and coupled symmetrical striplines are presented. The numerical computations are simplified by the excellent convergence properties of Jacobi's theta functions.     

Analysis implications of the choice of a structural model in the nonequivalent control group design.

Reviews D. A. Kenny's (1975) general model and suggests an approach involving the use of multiple measures as an alternative means of achieving identification. The multiple measures approach has potential advantages where program assignment to the treatment condition is based on group differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of forage type, ratio of forage to concentrate, and methionine hydroxy analog on performance of dairy cows.

In a 2-yr study, 44 primiparous and 77 multiparous cows were assigned to one of 12 dietary treatments (2 X 3 X 2 factorial). Treatments were two forages (alfalfa or smooth bromegrass), three percentages of grain (40, 50 or 60% of diet DM), and two percentages of methionine hydroxy analog (0 or .15% of diet DM). Feeds were offered as total mixed diets. Data collection began 4 d postpartum and continued through 116 d postpartum. Dry matter intake was not affected by percentage of concentrate or forage source even though NDF of the diets ranged from 25.6 to 48.8% and ADF ranged from 15.7 to 36.8%. Cows fed bromegrass hay produced 1.5 kg/d more FCM and 1.2 kg/d more SCM than those fed alfalfa hay. Concentrate percentage in the diet increased milk yield (28.9, 30.4 and 31.3 kg/d at 40, 50 and 60%, respectively). Methionine hydroxy analog increased milk fat percentage and yield for cows fed diets of 50 and 60% concentrate with alfalfa hay but not for those fed diets of 50 and 60% concentrate with bromegrass hay. Effect of methionine hydroxy analog was not significant for milk fat or yield when diets of 40% concentrate were fed.     

Asymmetry of inference in the dishabituation paradigm.

The habituation paradigm is frequently used to assess cognitive development in infants. Habituation to a stimulus by repeated presentation, followed by dishabituation (increased attention to a novel stimulus) is taken to imply discriminability of the novel stimulus. However, infants do not always dishabituate, even when the old and new stimuli are known to be discriminable. It is postulated that failure of dishabituation could be due either to a lack of discriminability of the new stimulus or to failure to relate it to the schema elaborated during habituation. Support for this postulate was obtained in 4 experiments with a total of 200 infants ranging in age from 5.5 to 29 mo. The materials varied from geometric forms through auditory stimuli to conceptual categories. In some cases dishabituation did not occur despite the known discriminability of familiar and novel stimuli. The degree of attention directed toward the new stimulus might better be understood in terms of the degree of discrepancy between the unfamiliar stimulus and the schema for the familiar (the curvilinear discrepancy hypothesis) rather than the ease of discriminability between old and new stimuli. (French abstract) (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)