Presentation of three different viral peptides, HTLV-1 Tax, HCMV gB, and influenza virus M1, is determined by common structural features of the HLA-A2.1 molecule.

To determine whether similar or dissimilar molecular features of class I molecules are involved in the presentation of structurally distinct peptides, we have investigated the influence of different pockets of the HLA-A2.1 molecule on the presentation of three different viral peptides. HTLV-I Tax peptide 12-19, HCMV gB 619-628, and influenza M1 58-66 are minimal peptides that induce HLA-A2.1-restricted noncross-reactive CTL. A detailed analysis of the structural features of HLA-A2.1 that are involved in peptide presentation was undertaken using a panel of 11 HLA-A2 mutants with single amino acid substitutions within pockets present in the peptide binding site. Nine of the 11 mutants affected presentation of each of the three peptides, whereas the other two mutants had negative effects on presentation of only two of these viral peptides. These results indicate that common structural features in HLA-A2 determine the binding of different peptides, and help to provide a plausible explanation for how structurally diverse peptides bind to HLA-A2.     

Immunocytochemical characterization of a new marker of fibrous and reactive astrocytes

A specific monoclonal antiserum (Mab 6.17) inducing a strong immunostaining of the neuromuscular junction has been used to detect the possible occurrence of the corresponding antigen throughout the intact or lesioned central nervous system of adult rats. In intact animals, 6.17-immunolabeling was essentially detected in astrocyte-like structures located in white matter fasciculi of the brain, such as the optic tract, corpus callosum, fornix, and in the white matter of the spinal cord. The astroglial nature of such 6.17-immunolabeled profiles was verified by performing double or triple immunofluorescent labeling with Mab 6.17 and with specific antisera against astrocytic markers, such as S100 protein, glial fibrillary acidic protein and vimentin. In the white matter, all the structures reactive to Mab 6.17 were also reactive to antibodies against S100 protein, glial fibrillary acidic protein and vimentin. On the other hand, astrocytes of the grey matter that were immunoreactive to S100 and glial fibrillary acidic protein but negative to vimentin, were devoid of 6.17-immunoreactivity. After lesions including stab wound through the diencephalon or transection of the spinal cord, a marked increase of 6.17-immunostaining was noted in the regions surrounding the lesions. In these regions, 6.17-immunolabeling was associated with S100-, GFAP- and vimentin-positive astrocytes constituting the glial scar. The ultrastructural localization of 6.17-immunoreactivity indicated that, similar to glial fibrillary acidic protein and vimentin, the recognized antigen was mainly associated with gliofilaments. These observations indicate that, in the central nervous system of adult rats, Mab 6.17 recognizes a molecule associated with gliofilaments, which is essentially associated to reactive astrocytes expressing high levels of vimentin. Received: 2 May 1995 / Accepted: 31 July 1995     

Host preferences and behaviour of oxpeckers: co-existence of similar species in a fragmented landscape

The host preferences and behaviour of red-billed and yellow-billed oxpeckers (Buphagus erythrorynchus and Buphagus africanus) were studied at two locations in Kenya and combined with previously published data from East and South Africa. Red-billed oxpeckers are generally more common and have a greater niche breadth with respect to host preferences than yellow-billed oxpeckers, possibly due to the behavioural dominance of the latter. Otherwise, the host preferences are remarkably similar: both prefer larger species of ungulates and are found predominantly on species with manes. There are also no significant differences in the time–activity budgets of the two species controlling for site and host species, and differences in the proportion of time spent on different body parts of hosts are small in absolute magnitude even when statistically significant. Despite these and other basic ecological similarities, no evidence for competitive displacement was detected by comparing host preferences in areas of sympatry with areas of allopatry, even though each species appears to depress the population size of the other when sympatric. Traditional single-community competition theory cannot explain the geographical ecology of these two species. Instead, co-existence appears to be dependent on the patterns of extinction and colonization characterized by metapopulations distributed among a fragmented habitat.     

Shade adaptation in cyanobacteria

Growth of Anacystis in high light in the presence of sublethal concentrations of DCMU-type inhibitors leads to an increased synthesis of phycocyanin paralleled by a reduced rate of ³⁵S methionine incorporation into the D1 protein compared to the high light controls, as is characteristic for naturally-induced shade phenotype. On the contrary, sun phenotype is characterized by a low rate of antenna synthesis, but a high rate of ³⁵S methionine incorporation into the D1 protein.Room temperature excitation spectra of 684 nm fluorescence emission clearly demonstrate the participation of the extraordinarily high concentration of phycocyanin in artificially shade-adapted cells in excitation energy transfer to chlorophyll.It could be shown that the development of shade-type appearance is not simply the consequence of an imbalance in electron transport, since an addition of thiosulphate to cultures growing in high light in the presence of DCMU-type inhibitors can only partially prevent or revert the change from sun to artificial-herbicide-induced-shade phenotype. This is regarded as evidence that the dynamic herbicide-binding D1 protein itself may play a role as a light meter in the process of natural shade adaptation, the rate of its degradation and resynthesis possibly giving the signal for the adaptive reorganization of the photosynthetic apparatus. The chain of signal transduction remains to be established.Abbreviations atrazine 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine - chl chlorophyll - D1 reaction center polypeptide carrying the secondary plastoquinone electron acceptor of PS II - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PAGE polyacrylamide gel electrophoresis - PAR photosynthetically active radiation - PC phycocyanin - PCC Pasteur Culture Collection - PS photosystem - Q_B secondary plastoquinone electron acceptor of PS II - SAUG Sammlung von Algenkulturen am Pflanzenphysiologischen Institut der Universtität Göttingen - SDS sodium dodecyl sulphate Dedicated to Professor Wilhelm Menke on the occasion of his 80th birthday.