The plasminogen polymorphism in South African Negro populations: genetics and anthropogenetics

Summary Genetic polymorphism of human plasminogen (PLG) was investigated in 1252 unrelated individuals from eight South African Bantu-speaking Negro tribes. PLG phenotypes were determined by isoelectric focusing (pH 3.5–9.5 and 5–8 gradients) of neuraminidase-treated samples and subsequent detection by caseinolytic overlay or immunoblotting with specific antibody. No significant difference in the distribution of PLG alleles among the eight ethnic groups was observed. The combined allele frequencies of the common alleles in South African Negroes were 0.6977 for PLG*A, 0.2736 for PLG*B. In addition, six rare alleles were seen: PLG*A3, *A1, *M2, *B1, *B2, *B3. The rare variant PLG*B2 was proven to segregate by autosomal Mendelian inheritance in a family. The combined frequency for the rare alleles was 0.0287. The distribution of phenotypes in the total population sample was found to be in Hardy-Weinberg equilibrium. A striking difference in PLG allele distribution between Negroes from South Africa and published Negroid frequencies from North America could be observed. This difference was also seen in comparison with Mongoloid populations; in contrast, PLG frequencies for South African Negroes were similar or almost identical to known Caucasoid distributions.     

Molecular analysis of theArabidopsis pattern formation geneGNOM: gene structure and intragenic complementation

TheGNOM gene is required for pattern formation along the main body axis of the embryo in the flowering plantArabidopsis thaliana. Mutations in theGNOM gene alter the asymmetric division of the zygote and interfere with the formation of distinct apical-basal regions in the developing embryo. We have isolated theGNOM gene by positional cloning, characterised its structure and determined the molecular lesions in mutant alleles. Although the predicted 163 kDa GNOM protein has a conserved domain in common with the yeast secretory protein Sec7p, it is most closely related in size and overall similarity to the product of the yeastYEC2 gene, which is not essential for cell viability. Four fully complementinggnom alleles carry missense mutations in conserved regions, seven partially complementing alleles have premature stop codon mutations and two non-complementing alleles have splice-site lesions. Our results suggest that the GNOM protein acts as a complex of identical subunits and that partial complementation may involve low levels of full-length protein generated by inefficient translational read-through.Communicated by H. Saedler     

Localization of proteasomes in plant cells

Summary Proteasomes, also known as multicatalytic proteinase complexes, were localized in suspension cells of potato (Solanum tuberosum) by direct immunofluorescence using polyclonal antibodies labelled with fluorescein isothiocyanate. The method used allows an estimate of relative amounts of proteasomal antigens in different cell components. Proteasomes are present in the nuclei and the cytoplasm. The nucleoplasm contains small areas of weak fluorescence. The peripheral cytoplasm and possibly elements of the cytoskeleton show higher fluorescence than other parts of the cytoplasm. This indicates a localization of proteasomes similar to that known from animal cells.Abbreviations DMSO dimethylsulfoxide - EGTA ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetra acetic acid - FITC fluorescein isothiocyanate - PBS phosphate buffered saline - PIPES piperazine-1,4-bis-(2-ethanesulfonic acid)     

Cellular location,activity states,and macromolecular organization of glucoamylase in Clostridium thermosaccharolyticum

By application of immunocytochemical techniques at the electron microscope level, glucoamylase was localized to the cell periphery in Clostridium thermosaccharolyticum during and following growth on starch, sucrose or glucose. Levels of immunolabelling were found to be relatively independent of growth substrate and of phase of growth, whereas previous studies had demonstrated strong dependence of glucoamylase activity on growth conditions; previously high levels of glucoamylase activity had been detected after growth on starch (i.e. during the stationary phase after growth) and only very low activities detected during exponential growth and following growth on glucose. The results presented demonstrate that levels of the glucoamylase protein are independent of measurable enzyme activity, and imply that the protein is constitutive. This indicates that the protein can exist in active and inactive states in the cell. By analogy with similar systems, we consider it likely that maturation or activation of newly synthesized glucoamylase occurs during (or following) transport through the cytoplasmic membrane. Electron microscopy of individual protein molecules which had been subjected to negative staining revealed that the enzyme consists of two domains of approximately equal size which are linked by a hinge region.     

Motor learning

Bilateral damage of the medial temporal lobe system prevents the formation of new declarative memories but leaves intact knowledge that was acquired before damage. For motor learning, no structure has been identified that plays a comparable role for the consolidation of motor memories. The deficits of motor learning are focal and show a similar allocation to the various of motor learning are focal and show a similar allocation to the various sensorimotor subsystems, as do the corresponding non-mnemonic functions. The involvement of sensorimotor circuitries changes during motor learning so that association areas are preferentially activated in the early stages, and cerebello- and striato-motor-cortical loops are preferentially activated in the late stages of motor learning. Recent neuroanatomical and neurophysiological findings on the effects of brain lesions in human and non-human primates are discussed.