Respiratory syncytial virus (RSV) SH and G proteins are not essential for viral replication in vitro: clinical evaluation and molecular characterization of a cold-passaged, attenuated RSV subgroup B mutant.

A live, cold-passaged (cp) candidate vaccine virus, designated respiratory syncytial virus (RSV) B1 cp-52/2B5 (cp-52), replicated efficiently in Vero cells, but was found to be overattenuated for RSV-seronegative infants and children. Sequence analysis of reverse-transcription-PCR-amplified fragments of this mutant revealed a large deletion spanning most of the coding sequences for the small hydrophobic (SH) and attachment (G) proteins. Northern blot analysis of cp-52 detected multiple unique read-through mRNAs containing SH and G sequences, consistent with a deletion mutation spanning the SH:G gene junction. Immunological studies confirmed that an intact G glycoprotein was not produced by the cp-52 virus. Nonetheless, cp-52 was infectious and replicated to high titer in tissue culture despite the absence of the viral surface SH and G glycoproteins. Thus, our characterization of this negative-strand RNA virus identified a novel replication-competent deletion mutant lacking two of its three surface glycoproteins. The requirement of SH and G for efficient replication in vivo suggests that selective deletion of one or both of these RSV genes may provide an alternative or additive strategy for developing an optimally attenuated vaccine candidate.

A live attenuated bovine parainfluenza virus type 3 vaccine is safe, infectious, immunogenic, and phenotypically stable in infants and children.

The safety, infectivity, immunogenicity, transmissibility, and phenotypic stability of an intranasal bovine parainfluenza virus type 3 (BPIV-3) candidate vaccine was evaluated in a randomized, double-blind, placebo-controlled trial. Of human parainfluenza virus type 3 (HPIV-3)-seronegative children, 92% were infected, and 92% developed a serum hemagglutination-inhibiting (HAI) antibody response to BPIV-3 and 61% to HPIV-3. Geometric mean HAI titers were 1:40 to BPIV-3 and 1:16 to HPIV-3. In studies to evaluate vaccine transmissibility, none of 14 placebo recipients in close contact with 14 vaccinees shed BPIV-3. BPIV-3 isolates from seronegative vaccinees retained the attenuation phenotype when tested in rhesus monkeys. Although it is difficult to evaluate the safety and immunogenicity of such a vaccine in an open population of children who frequently become infected with HPIV-3, it appears that the live BPIV-3 vaccine is attenuated, infectious, immunogenic, poorly transmissible, and phenotypically stable and warrants further evaluation as a candidate vaccine in infants and children.

Delay of cell differentiation in Anabaena aequalis caused by UV-B radiation and the role of photoreactivation and excision repair.

The effect of ultraviolet light on cell differentiation was studied in the cyanobacterium Anabaena aequalis. Exposure of cells to UV-B wavelengths (280-320 nm) significantly delayed the differentiation of vegetative cells into heterocysts and akinetes at doses up to 56 kJ m-2. Heterocyst differentiation was essentially stopped at all exposure levels when photoreactivation was prevented, even when excision repair was available to the cells. Photoreactivated samples produced heterocysts at doses through 28 kJ m-2, after which differentiation dropped steeply to near zero levels. Some recovery of differentiation was evident at higher doses but at levels much below that of controls. Akinete differentiation was only slightly delayed by the exposures when cells were photoreactivated. Samples then showed rapid differentiation with the numbers of akinetes significantly greater than controls. Cells that did not receive photoreactivating light showed a greater initial delay in differentiation but 2 weeks after the exposures had recovered to control levels. Caffeine had more effect on the differentiation of akinetes than heterocysts. Inhibition of excision repair greatly reduced differentiation in photoreactivated samples and essentially eliminated differentiation in the nonphotoreactivated samples.

Multichannel acousto-optic crossbar switch with arbitrary signal fan-out.

We propose an N x N acousto-optic switch architecture capable of arbitrary signal fan-out with O(N logN) hardware complexity. We also investigate the impact of signal fan-out on loss and cross talk.

Multichannel acousto-optic crossbar switch.

We analyze an acousto-optic crossbar switch architecture that can be used to implement an N x N point-to-point switch with just N hardware complexity. In our analysis, we determine that insertion loss and cross talk are minimized if we place the output ports in the diffraction far field of the acousto-optic cell. Using this result, we develop an optimum switch design based on Fourier optics: a Fourier transform lens is used both to scale the output beams for efficient coupling to the output ports and to provide a necessary optical fan-in from input to output ports. We demonstrate the performance of switch configurations using single-mode fiber input ports in conjunction with single-mode fiber, multimode fiber, and photodiode output ports.

Acousto-optic photonic switch.

An acousto-optic architecture is presented to implement a nonblocking space-division switch with O(N) complexity. Signal degradation is minimal so that the switch is suitable for nonregenerative application within optical networks; it is also capable of rapid reconfiguration. Experiments for a 1 x 4 switch show an insertion loss ranging from 4.6 to 5.6 dB, a worst-case signal-to-cross-talk ratio of better than 30 dB, and a reconfiguration time of 1.46 microsec.

On the concept of orbital steering in catalytic reactions.

Angular displacement from linear overlap of but a few degrees in the transition state of the enzyme-substrate complex has been postulated to be of great kinetic significance ("orbital steering"). The concept of orbital steering is shown to have evolved from the orientation parameters of an equation previously proposed to evaluate the kinetic importance of propinquity. This equation is shown to be naive. Arguments provided against the concept of orbital steering include: (a) force constants predicted from orbital steering are about 100 times those experimentally determined from displacement of nuclei in a direction normal to the axis of a covalent bond (for example, at room temperature vibrational bending amplitudes of +5 degrees or more are common); (b) because of the lessened directionality of orbitals containing nonbonded electron pairs, the force constants in transition states should be even smaller than in the case of a covalent bond; and (c) molecular orbital calculations predict shallow total energy minima for orbital alignment. The experimental rate data offered as a basis for the concept of orbital steering are shown to find rationalization in the previously observed dependence of DeltaSdouble dagger on kinetic order and the energy requirements for the freezing-out of single bonds in the transition state leading to the formation of medium-size ring compounds from extended ground states. It is concluded that if orbital steering does exist, experimental and theoretical evidence to support this concept have yet to be presented.

An Autoinhibitory Substance Produced by Platydorina caudata Kofoid.

An inhibitory substance was obtained from culture filtrates of Platydorina caudata Kofoid, (a colonial, green flagellate), in which death of the culture had occurred. The cessation of growth occurs before, and is seemingly independent of, medium depletion. The substance can be detected as early as the 15th day, and by the 25th day growth is completely suppressed. A bioassay method for quantitating the activity of the substance was devised. The substance is heat-labile, nondialyzable, acid-labile, and apparently specific for Platydorina. The substance resists short periods of freezing and bacterial contamination. Preliminary results suggest that trypsin destroys activity of the substance.

NUTRITION OF PLATYDORINA CAUDATA KOFOID.

The vitamins p-aminobenzoic acid, thiamine, biotin, nicotinamide, and B12 were tested for their ability to stimulate growth. Only vitamin B12 was required. Urea and NaNO2 supported excellent growth, although sodium nitrite, ammonium nitrate, and the Casamino acids supported only fair growth. Platydorina grew aerobically in the absence of an exogenous source of carbon; however a carbon source was required for anaerobic growth. Of 25 carbon compounds examined, isocitrate supported anaerobic growth in the light equalling the aerobic controls. Growth did not occur aerobically or anaerobically in the dark with any carbon source examined. Growth was excellent at pH values in excess of 7.0. Growth at pH 10.0 was 4 times that at 7.0 in strain I.U. 850 and twice that at 7.0 in strain Kan-3E. Growth was accelerated with the increase in temperatures but this increase may well be due to the increased intensity of light to which the cultures were exposed at the higher terperatures.