env sequences of simian immunodeficiency viruses from chimpanzees in Cameroon are strongly related to those of human immunodeficiency virus group N from the same geographic area

Human immunodeficiency virus type 1 (HIV-1) group N from Cameroon is phylogenetically close, in env, to the simian immunodeficiency virus (SIV) cpz-gab from Gabon and SIVcpz-US of unknown geographic origin. We screened 29 wild-born Cameroonian chimpanzees and found that three (Cam3, Cam4, and Cam5) were positive for HIV-1 by Western blotting. Mitochondrial DNA sequence analysis demonstrated that Cam3 and Cam5 belonged to Pan troglodytes troglodytes and that Cam4 belonged to P. t. vellerosus. Genetic analyses of the viruses together with serological data demonstrated that at least one of the two P. t. troglodytes chimpanzees (Cam5) was infected in the wild, and revealed a horizontal transmission between Cam3 and Cam4. These data confirm that P. t. troglodytes is a natural host for HIV-1-related viruses. Furthermore, they show that SIVcpz can be transmitted in captivity, from one chimpanzee subspecies to another. All three SIVcpz-cam viruses clustered with HIV-1 N in env. The full Cam3 SIVcpz genome sequence showed a very close phylogenetic relationship with SIVcpz-US, a virus identified in a P. t. troglodytes chimpanzee captured nearly 40 years earlier. Like SIVcpz-US, SIVcpz-cam3 was closely related to HIV-1 N in env, but not in pol, supporting the hypothesis that HIV-1 N results from a recombination event. SIVcpz from chimpanzees born in the wild in Cameroon are thus strongly related in env to HIV-1 N from Cameroon, demonstrating the geographic coincidence of these human and simian viruses and providing a further strong argument in favor of the origin of HIV-1 being in chimpanzees.     

Heteroduplex mobility assay as a tool for predicting phylogenetic affiliation of environmental ribosomal RNA clones

Heteroduplex mobility assay (HMA) of partial 16S rRNA gene fragments was tested as a tool for predicting bacterial phylogenetic relationships. Approximately 400-bp fragments were amplified from a selection of cloned environmental DNAs representing a range of sequence identities and phylogenetic relationships. Heteroduplexes between pairs of sequences were formed by mixing equal amounts of PCR products, denaturing and annealing. Annealed mixes were separated on 8% polyacrylamide gels and silver stained. Heteroduplexes were readily distinguished from reannealed homoduplex and unannealed fragments in all sequences where percentage identity was less than 95%. The heteroduplexes showed retarded electrophoretic migration with respect to homoduplexes. The relative retardation was strongly correlated to the percentage sequence identity between the two strands. The HMA is a useful tool for screening environmental clone libraries to systematically select clones representative of the phylogenetic diversity within the sample, or to selectively retrieve members of a particular phylogenetic group for more detailed study.     

Study of Toxin Production by Isolates of Stachybotrys chartarum and Memnoniella echinata Isolated during a Study of Pulmonary Hemosiderosis in Infants

A cluster of cases of pulmonary hemosiderosis among infants was reported in Cleveland, Ohio, during 1993 and 1994. These unusual cases appeared only in infants ranging in age from 1 to 8 months and were characterized by pulmonary hemorrhage, which caused the babies to cough up blood. A case-control study identified major home water damage (from plumbing leaks, roof leaks, or flooding) as a risk factor for development of pulmonary hemorrhage in these infants. Because of an interest in the possibility that trichothecene mycotoxins might be involved in this illness, a number of isolates of Stachybotrys chartarum were grown in the laboratory on rice, and extracts were prepared and analyzed both for cytotoxicity and for specific toxins. Two isolates of Memnoniella echinata, a fungus closely related to S. chartarum, were also included in these studies. S. chartarum isolates collected from the homes were shown to produce a number of highly toxic compounds, and the profiles of toxic compounds from M. echinata were similar; the most notable difference was the fact that the principal metabolites produced by M. echinata were griseofulvins.     

CO binding studies of nitric oxide synthase: effects of the substrate, inhibitors and tetrahydrobiopterin

The dissociation constant (K_d) for CO from neuronal nitric oxide synthase heme in the absence of the substrate and cofactor was less than 10⁻³ μM. In the presence of

Full-size image

-Arg, it dramatically increased up to 1 μM. In the presence of inhibitors such as N^G-nitro-

Full-size image

-arginine methyl ester and 7-nitroindazole (NI), the K_d value further increased up to more than 100 μM. Addition of the cofactor, 5,6,7,8-tetrahydrobiopterin (H₄B), increased the K_d value by 10-fold in the presence of

Full-size image

-Arg, whereas it decreased the value to less than one 250th in the presence of NI. Addition of H₄B increased the recombination rate constant (k_on) for CO by more than two-fold in the presence of

Full-size image

-Arg or N⁶-(1-iminoethyl)-

Full-size image

-lysine, whereas it decreased the k_on value by three-fold in the presence of

Full-size image

-thiocitrulline. Thus, the binding fashion of some of inhibitors, such as NI, may be different from that of

Full-size image

-Arg with respect to the H₄B effect.     

Calcium-Dependent Protein Phosphorylation May Mediate the Gibberellic Acid Response in Barley Aleurone

Peptide substrates of well-defined protein kinases were microinjected into aleurone protoplasts of barley (Hordeum vulgare L. cv Himalaya) to inhibit, and therefore identify, protein kinase-regulated events in the transduction of the gibberellin (GA) and abscisic acid signals. Syntide-2, a substrate designed for Ca²⁺- and calmodulin (CaM)-dependent kinases, selectively inhibited the GA response, leaving constitutive and abscisic acid-regulated events unaffected. Microinjection of syntide did not affect the GA-induced increase in cytosolic [Ca²⁺], suggesting that it inhibited GA action downstream of the Ca²⁺ signal. When photoaffinity-labeled syntide-2 was electroporated into protoplasts and cross-linked to interacting proteins in situ, it selectively labeled proteins of approximately 30 and 55 kD. A 54-kD, soluble syntide-2 phosphorylating protein kinase was detected in aleurone cells. This kinase was activated by Ca²⁺ and was CaM independent, but was inhibited by the CaM antagonist N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (250 μm), suggesting that it was a CaM-domain protein kinase-like activity. These results suggest that syntide-2 inhibits the GA response of the aleurone via an interaction with this kinase, implicating the 54-kD kinase as a Ca²⁺-dependent regulator of the GA response in these cells.     

Mapping the Functional Roles of Cap Cells in the Response of Arabidopsis Primary Roots to Gravity

The cap is widely accepted to be the site of gravity sensing in roots because removal of the cap abolishes root curvature. Circumstantial evidence favors the columella cells as the gravisensory cells because amyloplasts (and often other cellular components) are polarized with respect to the gravity vector. However, there has been no functional confirmation of their role. To address this problem, we used laser ablation to remove defined cells in the cap of Arabidopsis primary roots and quantified the response of the roots to gravity using three parameters: time course of curvature, presentation time, and deviation from vertical growth. Ablation of the peripheral cap cells and tip cells did not alter root curvature. Ablation of the innermost columella cells caused the strongest inhibitory effect on root curvature without affecting growth rates. Many of these roots deviated significantly from vertical growth and had a presentation time 6-fold longer than the controls. Among the two inner columella stories, the central cells of story 2 contributed the most to root gravitropism. These cells also exhibited the largest amyloplast sedimentation velocities. Therefore, these results are consistent with the starch-statolith sedimentation hypothesis for gravity sensing.     

Accelerated Evolution of Cytochrome b in Simian Primates: Adaptive Evolution in Concert with Other Mitochondrial Proteins?

We have sequenced the cytochrome b gene of Horsfield's tarsier, Tarsius bancanus, to complete a data set of sequences for this gene from representatives of each primate infraorder. These primate cytochrome b sequences were combined with those from representatives of three other mammalian orders (cat, whale, and rat) in an analysis of relative evolutionary rates. The nonsynonymous nucleotide substitution rate of the cytochrome b gene has increased approximately twofold along lineages leading to simian primates compared to that of the tarsier and other primate and nonprimate mammalian species. However, the rate of transversional substitutions at fourfold degenerate sites has remained uniform among all lineages. This increase in the evolutionary rate of cytochrome b is similar in character and magnitude to that described previously for the cytochrome c oxidase subunit II gene. We propose that the evolutionary rate increase observed for cytochrome b and cytochrome c oxidase subunit II may underlie an episode of coadaptive evolution of these two proteins in the mitochondria of simian primates. Received: 15 December 1997 / Accepted: 24 February 1998     

Effect of aluminum on cytoplasmic Ca2+ homeostasis in root hairs of Arabidopsis thaliana (L.)

Aluminum inhibition of root growth is a major world agricultural problem where the cause of toxicity has been linked to changes in cellular calcium homeostasis. Therefore, the effect of aluminum ions (Al) on changes in cytoplasmic free calcium concentration ([Ca²⁺]_c) was followed in root hairs of wild-type, Al-sensitive and Al-resistant mutants of Arabidopsis thaliana (L.) Heynh. Generally, Al exposure resulted in prolonged elevations in tip-localized [Ca²⁺]_c in both wild-type and Al-sensitive root hairs. However, these Al-induced increases in [Ca²⁺]_c were not tightly correlated with growth inhibition, occurring up to 15 min after Al had induced growth to stop. Also, in 32% of root hairs examined growth stopped without a detectable change in [Ca²⁺]_c. In contrast, Al-resistant mutants showed little growth inhibition in response to AlCl₃ exposure and in no case was a change in [Ca²⁺]_c observed. Of the other externally applied stresses tested (oxidative and mechanical stress), both were found to inhibit root hair growth, but only oxidative stress (H₂O₂, 10 μM) caused a prolonged rise in [Ca²⁺]_c similar to that induced by Al. Again this increase occurred after growth had been inhibited. The lack of a tight correlation between Al exposure, growth inhibition and altered [Ca²⁺]_c dynamics suggests that although exposure of root hairs to toxic levels of Al causes an alteration in cellular Ca²⁺ homeostasis, this may not be a required event for Al toxicity. The elevation in [Ca²⁺]_c induced by Al also strongly suggests that the phytotoxic action of Al in root hairs is not through blockage of Ca²⁺-permeable channels required for Ca²⁺ influx into the cytoplasm. Received: 24 October 1997 / Accepted: 6 March 1998