The matrix protein of human immunodeficiency virus type 1 is required for incorporation of viral envelope protein into mature virions.

Accumulating evidence suggests that the matrix (MA) protein of retroviruses plays a key role in virus assembly by directing the intracellular transport and membrane association of the Gag polyprotein. In this report, we show that the MA protein of human immunodeficiency virus type 1 is also critical for the incorporation of viral Env proteins into mature virions. Several deletions introduced in the MA domain (p17) of human immunodeficiency virus type 1 Gag polyprotein did not greatly affect the synthesis and processing of the Gag polyprotein or the formation of virions. Analysis of the viral proteins revealed normal levels of Gag and Pol proteins in these mutant virions, but the Env proteins, gp120 and gp41, were hardly detectable in the mutant virions. Our data suggest that an interaction between the viral Env protein and the MA domain of the Gag polyprotein is required for the selective incorporation of Env proteins during virus assembly. Such an interaction appears to be very sensitive to conformational changes in the MA domain, as five small deletions in two separate regions of p17 equally inhibited viral Env protein incorporation. Mutant viruses were not infectious in T cells. When mutant and wild-type DNAs were cotransfected into T cells, the replication of wild-type virus was also hindered. These results suggest that the incorporation of viral Env protein is a critical step for replication of retroviruses and can be a target for the design of antiviral strategies.     

Karyotypes of Pneumocystis carinii from Korean rats.

Molecular karyotyping was applied to Pneumocystis carinii(Pc) from two strains of experimental rats, Sprague Dawley(SD) and Fisher(F), in Korea. Field inversion gel electrophoresis and contour clamped homogeneous electric field electrophoresis resolved 15 chromosomal bands from the Pc. The size of the bands was estimated 270kb to 684kb from SD rats, and 273kb to 713 kb from F rats. The bands of 283 kb from SD rats and of 273 kb from F rats stained more brightly suggesting duplicated bands. Total number of chromosomes was at least 16, and total genomic size was estimated 7 x 10(6) bp. All of the bands from F rats hybridized to the probe of repeated DNA sequences of Pc and the band of 448 kb size was proved to contain rDNA sequences, but Pc. chromosome bands from SD rats showed no reactions to the probes. The 2 different karyotypes of P. carinii from 2 strains of rats were maintained consistently for 2 years.     

Stomatal responses to light in the facultative Crassulacean acid metabolism species, Portulacaria afra

Guard cell responses to light are mediated by guard cell chlorophyll and by a specific blue light photoreceptor. Gas exchange and epidermal peel techniques were employed to investigate these responses in the facultative Crassulacean acid metabolism (CAM) species, Portulacaria afra (L.) Jacq. In P. afra individuals performing C₃ metabolism, red light stimulated an increase in leaf conductance in intact leaves and stomatal opening in isolated epidermal peels, indicating the presence in guard cells of the chlorophyll-mediated response to light. Under a background of continuous red illumination, conductance exhibited transient increases following pulses of blue but not red light, indicating that the specific stomatal response to blue light was also operative. In contrast, in CAM individuals, conductance in gas exchange experiments and stomatal opening in epidermal peel experiments were not stimulated by red light. In CAM plants, conductance did not increase following blue light pulses administered over a range of temperatures, vapor pressure differences (VPD), ambient CO₂ concentrations and background red light intensities. These results indicate that P. afra does possess typical guard cell responses to light when performing C₃ metabolism. The metabolic pathways mediating these responses are either lost or inhibited when CAM is induced.     

Effect of photobioreactor inclination on the biomass productivity of an outdoor algal culture

The profiles of photon flux density incidented on a tubularloop photobioreactor in the day could be altered by inclining the bioreactor at an angle with the horizontal. The photon flux density at noon decreased with increasing angle of inclination, whereas the photon flux density in the early morning and late afternoon increased with increasing angle of inclination. The overall photosynthetic radiance received by the bioreactor inclined at 0, 25, 45, and 80 degrees was 1:0.89:0.77:0.62. Regardless of the angle of bioreactor inclination, the overall biomass output rate of a fed-batch culture over an 8-h/day period was comparable (26-36 g-biomass m(-2) bioreactor surface area day(-1)). As a bioreactor inclined at an angle occupied smaller land area, and daily biomass output rate per land area of a bioreactor inclined at 80 degrees (130 g-biomass m(-2) land) was about six times of that obtainable at horizontal position (21-g biomass m(-2) land). The bioenergetics growth yield from the absorbed photosynthetic radiance was not a constant but an inverse function of the photon flux density. The quasi-steady state chlorophyll content of the Chlorella cells varied between 36 and 63 mg g(-1) cells. Photoinhibition of the maximum photosynthetic capacity was not observed in this study.     

Gly-238-Ser substitution changes the substrate specificity of the SHV class A beta-lactamases

The SHV-type beta-lactamase SHV-2A is related to SHV-1 by a Gly-238-Ser replacement. Strains carrying SHV-2A are resistant to the third generation cephems cefotaxime and ceftizoxime, whereas those that carry SHV-1 are sensitive to these drugs. We present a kinetic analysis of a SHV-1 and SHV-2A enzymes, with the goal of gaining insight into the role of residue 238 in hydrolyzing cefotaxime and ceftizoxime. SHV-2A shows altered kinetic properties for a number of other cephems that also have heterocyclic side chains at the amino position of the 7-aminocephalosporanic acid nucleus (R1 side chain), including a significantly higher kcat/Km than does SHV-1 for cephaloridine, cephalothin, and cefotiam. Two cephems with straight chain R1 substitutions, cephalosporin C and cephacetrile, are not hydrolyzed more efficiently by SHV-2A. These results indicate that the Ser-238-Gly substitution increases the affinity toward cephems with a heterocyclic ring in the R1 side chain. In addition, the data for ampicillin and benzylpenicillin show that addition of a nitrogen to the second carbon of the R1 side chain of a penem results in a lower kcat/Km for SHV-2A relative to SHV-1. These data strongly suggest that the previously proposed hydrogen bond formation between Ser-238 and the second carbon nitrogen of cefotaxime is not an important factor in hydrolysis by SHV-2A. We propose that the Gly-238 to Ser-238 replacement in SHV-2A has altered the hydrophobic pocket so that it can better accommodate cephems with bulky R1 side chains.     

Preparation of enteric-coated microspheres of Mycoplasma hyopneumoniae vaccine with cellulose acetate phthalate: The effect of swine serum on micromeritic properties

Summary Cellulose acetate phthalate was used to prepare the Mycoplasma hyopneumoniae vaccine (MHV) microspheres using a solvent evaporation method. Swine serum was used as an additive in the antigen to form the core materials. The addition of serum had a significant effect on surface topography of the MHV microspheres. By using this modified solvent evaporation method, the recoveries of antigens in the MHV microspheres were generally over 90% of the weight and antigenicity of antigens originally added in the formulation.     

Expression of the alpha, beta II, and gamma protein kinase C isozymes in the baculovirus-insect cell expression system. Purification and characterization of the individual isoforms

Detailed in vitro comparisons of the biochemical characteristics of three protein kinase C isozymes were performed. As an alternative to earlier uncertain separation methods and expression schemes, highly purified and genetically distinct protein kinase C enzymes were produced using the baculovirus expression system. The baculovirus expression system yielded approximately 200-300 micrograms of the purified isozyme from 3 x 10(8) (100 ml of culture medium) baculovirus-infected insect cells. Biochemical characterization of the expressed isozymes indicated that the three isozymes had virtually indistinguishable Ca2+, Mg2+, and ATP dependencies. However, in certain critical functional characteristics such as phosphatidylserine dependencies, phospholipid and substrate preferences, and arachidonic acid activation, the gamma isozyme exhibited distinctive properties when compared with both the alpha and beta II subtypes. In addition, the activity of the beta II subtype was more dependent upon diacylglycerol or phorbol esters for activation than either the alpha or gamma isoforms. The alpha isozyme, unlike the beta II and gamma forms, was totally dependent on Ca2+ for activation in the presence of free arachidonic acid. These studies provide definitive characterizations of the pure isoforms; many of the findings were consistent with earlier enzymatic observations using hydroxyapatite-purified isoforms. Thus, the distinctive biochemical properties of the protein kinase C isozymes are consistent with the hypothesis that each isoform may have distinct roles in signal transduction processes.     

Alteration of plasmid DNA-mediated transformation and mutation induced by covalent binding of benzo[a]pyrene- 7,8-dihydrodiol-9,10-oxide in Escherichia coli

Plasmid-mediated transformation and mutagenesis induced by (±)-trans- benzo[a]pyrene-7,8-dihydrodiol-9,10-oxide (BP-DEI) in recipient Escherichia coli (E. coli) have been studied. Because plasmid DNA is used, the system is entirely free from direct toxic effects of BP-DEI on the recipient cells. Plasmid pK0482 DNA, which has two dominant genes, β-lactamase (amp-r) and galactokinase (galK) was modified with BP-DEI prior to its transformation of E. coli N99, AB1157, AB2463(recA^?) and AB1886(uvrA^?). Transformants were selected by ampicillin resistance and mutations were analyzed simultaneously by the altered expression of the galK gene. (1) Approx. 3 molecules of BP-DEI per molecule of pK0482 DNA decreased the transformation efficiency to 37% in AB1157 and the mutation frequency in this strain was proportional to the amount of BP-DEI covalently bound to pK0482 DNA. (2) In AB1886(uvrA^?) a 37% transformation efficiency was produced by only 1 molecule of BP-DEI per molecule of pK0482 DNA, and the mutation frequency in this strain was higher than in AB1157. (3) In AB2463(recA^?), the transformation efficiency was similar to that obtained with AB1157, but mutagenesis was clearly suppressed. (4) Polyacrylamide gel patterns of restriction digests of the pK0482 mutated at the galK gene were indistinguishable from those of the unmutated plasmid DNA.