Image plane detector spectrophotometer: construction and nightglow observations

Following the theoretical simulation of an image plane detector spectrophotometer (IPDS) presented in a previous paper, a ground-based IPDS for airglow measurements is constructed. This low resolution spectrometer can measure a molecular band spectrum at 12 wavelength positions simultaneously without mechanical scan. The band brightness and rotational temperature of the emitter can be obtained from the measurements. We describe the optical design and calibration of the instrument and present some results of mesospheric nightglow observations. The evaluation and analysis on the performances of the new instrument are also given. The result shows that, although the constructed instrument does not represent the optimized IPDS, the instrument performed reasonably well, and with some improvements the IPDS has great potential of being used to study small-scale oscillations in airglow layers.

Crystallization and preliminary X-ray diffraction studies of Theiler's virus (GDVII strain)

Theiler's murine encephalomyelitis virus (TMEV) is a member of the picornavirus family. Mice infected with TMEV serve as models for the study of human neurological diseases including multiple sclerosis. Preparations of the GDVII strain of Theiler's virus have been crystallized using the hanging drop technique. When exposed to high intensity synchrotron radiation, these monoclinic crystals diffracted X-rays to at least 3.0 A resolution. The unit cell has a C-centered lattice with dimensions: a = 575.2 A, b = 324.0 A and c = 558.4 A, beta = 108.2 degrees. The molecular mass and cell dimensions imply that there is an entire virus particle per asymmetric unit, suggesting the presence of 60-fold non-crystallographic redundancy. This GDVII crystal form appears to be suitable for high-resolution structure determination.

Molecular cloning and analysis of a cDNA coding for the bifunctional dihydrofolate reductase-thymidylate synthase of Daucus carota

Molecular cloning of dihydrofolate reductase-thymidylate synthase (DHFR-TS) of Daucus carota was achieved by immunoscreening of a cDNA library obtaining a 2 kbp clone which contains an open reading frame of 1528 bp. Comparison of the deduced amino acid sequence with those from other sources revealed the presence of motifs typical of DHFR and TS thus confirming the bifunctional nature of the carrot protein. As in other organisms, a higher degree of conservation was observed in the TS domain. Analysis of the dhfr-ts gene content in carrot revealed the presence of several copies per diploid genome.

Molecular and structural basis of hemagglutination in mengovirus

The molecular and structural basis of mengovirus hemagglutination (HA) was investigated by the comparison of nucleotide sequences of the entire capsid coding regions of an HA+ variant, two HA- mutants, 205 and 280, and two HA+ revertants of 205. The mutants were selected after acridine mutagenesis of mengovirus-37A, a heat-stable and HA+ variant that is neurotropic in mice. HA+ revertants of mutant 205 were isolated from brain tissue of mice inoculated with mutant 205. The nucleotide sequences were determined by consensus RNA sequencing using genomic RNA templates from purified virions. Two nucleotide differences were observed in the VP1 coding region of the RNA genomes of mutants 205 and 280 in comparison to the RNA sequences of 37A and the revertants. Interpretation of these data predict substitutions of two consecutive amino acids at residues 1231 (K to R) and 1232 (P to S) of VP1 which form part of the H-I loop of VP1 found at the icosahedral fivefold axis. Analysis of the amino acid substitutions in the context of the three-dimensional structure of the mengovirus-M capsid indicated that hemagglutination most likely involves residues found at the icosahedral fivefold axis and probably does not involve the residues that form the putative cellular receptor binding site (the "pit"). Eleven amino acid differences were observed between the structural proteins of mengovirus-M and 37A, five in VP1, three in VP2, and three in VP3.

Characterization of a gene family encoding abscisic acid- and environmental stress-inducible proteins of alfalfa

The phytohormone abscisic acid (ABA) has been proposed as a common mediator controlling adaptive plant responses to a variety of environmental stresses, including water deficit, salinity, wounding, and low temperature. We have recently isolated three cDNAs, pUM90-1, pUM90-2, and pUM91-4, from a cDNA library of ABA-induced mRNAs of alfalfa. These cDNA clones exhibit a very high degree of sequence homology with one another and sequence similarities with certain regions of several stress- and ABA-inducible genes. The polypeptides encoded by these cDNAs are very rich in glycine (35-40%), histidine (7-15%), asparagine (8-14%), and tyrosine (5-10%) and have no tryptophan and proline. All of the encoded polypeptides contain characteristic tandem repeats comprising glycine residues intercepted with histidine and/or tyrosine. The RNAs corresponding to a representative cDNA, pUM90-1, were induced after treatment of seedlings with low temperature, drought, salt, and wounding stress, but not by heat; the induction was maximal under low temperature treatment. ABA and ABA analog rapidly induced the expression of these genes, whereas gibberellic acid treatment exhibited no induction whatsoever. These genes appear to be specifically induced in the shoot tissues. Analysis of ABA induction of genes corresponding to pUM90-1 in alfalfa seedlings of different age groups demonstrated that these genes were inducible in seedlings/plants of all age groups examined. Taken together these results suggest that these cDNA clones encode a group of proteins that are inducible by ABA and multiple environmental stresses and correspond to a new family of genes of plants, designated as ABA- and environmental stress-inducible genes.

Unusual diffraction of type B influenza virus neuraminidase crystals

An unusual X-ray diffraction pattern by tetragonal crystals of a type B influenza virus neuraminidase was observed in that the odd-l reflections were missing or diffuse while the even-l reflections were sharp and strong. A statistical analysis showed that an error (epsilon) in the spacing of successive planes of neuraminidase molecules was randomly distributed along the c direction, which resulted in such an unusual diffraction pattern. The error epsilon follows the Bernoullian distribution and may be caused by a flexible loop on the top surface of the neuraminidase.

Three-dimensional structure of Theiler murine encephalomyelitis virus (BeAn strain)

Depending on the strain, Theiler murine encephalomyelitis virus (TMEV) may cause acute encephalitis or chronic demyelinating disease, which is associated with viral persistence in mice. Persistent central nervous system infection and demyelination by the less-virulent TMEV has provided a useful animal model for the human demyelinating disease multiple sclerosis. The less-virulent BeAn strain of TMEV was crystallized and its atomic structure was determined by x-ray crystallography. The alpha-carbon coordinates of the closely related Mengo virus were used to calculate the initial phases to 3.5 A resolution and the interpretable electron density map was produced by 10 cycles of 30-fold noncrystallographic molecular replacement averaging. The structure revealed a high degree of overall structural similarity to Mengo virus as well as substantial differences in the surface loops. These structural changes might be correlated with TMEV host-specific recognition, pH-related stability, and neurovirulence.

Enzymatic activity of poliovirus RNA polymerase mutants with single amino acid changes in the conserved YGDD amino acid motif

RNA-dependent RNA polymerases contain a highly conserved region of amino acids with a core segment composed of the amino acids YGDD which have been hypothesized to be at or near the catalytic active site of the molecule. Six mutations in this conserved YGDD region of the poliovirus RNA-dependent RNA polymerase were made by using oligonucleotide site-directed DNA mutagenesis of the poliovirus cDNA to substitute A, C, M, P, S, or V for the amino acid G. The mutant polymerase genes were expressed in Escherichia coli, and the purified RNA polymerases were tested for in vitro enzyme activity. Two of the mutant RNA polymerases (those in which the glycine residue was replaced with alanine or serine) exhibited in vitro enzymatic activity ranging from 5 to 20% of wild-type activity, while the remaining mutant RNA polymerases were inactive. Alterations in the in vitro reaction conditions by modification of temperature, metal ion concentration, or pH resulted in no significant differences in the activities of the mutant RNA polymerases relative to that of the wild-type enzyme. An antipeptide antibody directed against the wild-type core amino acid segment containing the YGDD region of the poliovirus polymerase reacted with the wild-type recombinant RNA polymerase and to a limited extent with the two enzymatically active mutant polymerases; the antipeptide antibody did not react with the mutant RNA polymerases which did not have in vitro enzyme activity. These results are discussed in the context of secondary-structure predictions for the core segment containing the conserved YGDD amino acids in the poliovirus RNA polymerase.

The three-dimensional structure of canine parvovirus and its functional implications

The three-dimensional atomic structure of a single-stranded DNA virus has been determined. Infectious virions of canine parvovirus contain 60 protein subunits that are predominantly VP-2. The central structural motif of VP-2 has the same topology (an eight-stranded antiparallel beta barrel) as has been found in many other icosahedral viruses but represents only about one-third of the capsid protein. There is a 22 angstrom (A) long protrusion on the threefold axes, a 15 A deep canyon circulating about each of the five cylindrical structures at the fivefold axes, and a 15 A deep depression at the twofold axes. By analogy with rhinoviruses, the canyon may be the site of receptor attachment. Residues related to the antigenic properties of the virus are found on the threefold protrusions. Some of the amino termini of VP-2 run to the exterior in full but not empty virions, which is consistent with the observation that some VP-2 polypeptides in full particles can be cleaved by trypsin. Eleven nucleotides are seen in each of 60 symmetry-related pockets on the interior surface of the capsid and together account for 13 percent of the genome.

New crystalline forms of neuraminidase of type B human influenza virus

New crystalline forms of tetrameric neuraminidase heads from two strains (B/Lee/40 and B/mem/89) of type B human influenza virus were obtained and the crystals diffracted using X-rays to 2.5 A resolution without lattice disorder. The new B/Lee/40 crystalline form is tetragonal, space group P42(1)2, with unit cell dimensions a = 123.8 A, c = 71.8 A. The B/mem/89 crystalline form is also tetragonal, space group I422, with unit cell dimensions a = 122.9 A, c = 164.4 A. There is one neuraminidase monomer per asymmetric unit in both forms.

Antigenic, sequence, and crystal variation in influenza B neuraminidase

The neuraminidase (NA) genes of influenza B viruses B/Maryland/59, B/Hong Kong/8/73, B/Singapore/222/79, B/Oregon/5/80, B/USSR/100/83, B/Victoria/3/85, B/Leningrad/179/86, B/Memphis/6/86, and B/Memphis/3/89 have been sequenced. The deduced amino acid sequences show high variability in the stalk domain of the NA, but a surprising degree of sequence conservation in the head region which carries all the antigenic and enzyme activity. The variable region coding for the neuraminidase stalk also translates into a variable section in the overlapping NB polypeptide, which is coded from a second reading frame that overlaps the first 100 amino acids of NA. The influenza B NAs are antigenically distinguishable with monoclonal antibodies in neuraminidase-inhibition tests, even when there is only one amino acid sequence difference. However, seven of nine escape mutants selected with monoclonal antibodies were distinguished only by the antibody used for selection. When NA heads of influenza B viruses are crystallized, there are remarkable differences in crystal morphology between neuraminidases which have very few sequence changes.

Conformational variability of a picornavirus capsid: pH-dependent structural changes of Mengo virus related to its host receptor attachment site and disassembly

The structure of Mengo virus had been determined from crystals grown in the presence of 100 mM phosphate buffer at pH 7.4. It is shown that Mengo virus is poorly infectious at the phosphate concentration similar to that in which it was crystallized. Maximal infectivity is achieved at 10 mM phosphate or less in physiological saline. The phosphate effect is ameliorated when the pH is lowered to 4.6. Although it has not been possible to study the crystal structure of the virus at low phosphate concentrations, it is shown that increasing the Cl- concentration at pH 6.2 or decreasing the pH to 4.6 causes substantial conformational changes confined to the "pit," a deep surface depression. These structural changes involve a movement of the "FMDV loop" (GH loop) in VP1, an ordering of the "VP3 loop" (GH loop in VP3) between 3176 and 3182, the displacement of a bound phosphate near the "FMDV loop" (GH loop in VP1), and movement of the carboxy terminus of VP2. The changes in conformation are correlated with the dissociation of the virion into pentamers at pH 6.2 and 150 mM Cl-. The localization of the conformational changes and the correlated role of the phosphate in controlling infectivity support the hypothesis that the "pit" is the receptor attachment site.

Sindbis virus core protein crystals

The core protein of Sindbis virus has been crystallized. Three different crystal forms have been observed. They diffract variously from 2.5 A to 3.5 A resolution.