Abnormal interaction of the human apolipoprotein A-I variant [Lys107----0] with high density lipoproteins

Several isoforms of apoprotein A-I [apoA-I], the major apoprotein of high density lipoproteins [HDL], have been described. We compared the in vivo and in vitro properties of normal human apoA-I with those of apoA-I [Lys107----0]. Fluorescence and circular dichroic spectra showed that deletion of Lys107 decreases apoprotein self-association. In vivo metabolic studies in the rat indicated that the interaction of apoA-I [Lys107----0] with HDL was lower than normal. We conclude that deletion of Lys107 results in a reorganization of the apoprotein structure that decreases its potential to form hydrophobic associations.     

The transition point for protein synthesis in late S-G2 may be delayed by genome bromosubstitution without affecting the time of entry into mitosis

Bromosubstitution for most of the S period in synchronous populations of Allium cepa L. meristematic cells resulted in a delay in the late S-G2 transition point where protein synthesis is needed for later mitotic entrance to occur. This retardation in the position of the transition point was not accompanied by the expected delay in the entrance into mitosis, suggesting that such protein synthesis is a requisite, but not a timer for prophase triggering.     

Survival and activity of Salmonella typhimurium and Escherichia coli in tropical freshwater

The survival of Salmonella typhimurium LT2 and Escherichia coli was studied in situ in a tropical rain forest watershed using membrane diffusion chambers. Numbers were determined by acridine orange staining and a Coulter counter. Population activity was determined by microautoradiography, cell respiration, frequency of dividing cells, and by nucleic acid composition. Numbers of Salm. typhimurium and E. coli decreased less than 1 log unit after 105 h as measured by direct count methods. Activity as measured by respiration, acridine orange activity, frequency of dividing cells, and microautoradiography indicated that both bacteria remained moderately active during the entire study. After 24 h, E. coli was more active than Salm. typhimurium , as measured by nucleic acid composition, and frequency of dividing cells. Both E. coli and Salm. typhimurium survived and remained active in this tropical rain forest watershed for more than 5 d, suggesting that Salm. typhimurium may be of prolonged public health significance once it is introduced into tropical surface waters. As E. coli was active and survived for a long time in this natural environment, it would seem to be unsuitable as an indicator of recent faecal contamination in tropical waters.     

Characterization of the microtubule movement produced by sea urchin egg kinesin

We have used an in vitro assay to characterize some of the motile properties of sea urchin egg kinesin. Egg kinesin is purified via 5'-adenylyl imidodiphosphate-induced binding to taxol-assembled microtubules, extraction from the microtubules in ATP, and gel filtration chromatography (Scholey, J. M., Porter, M. E., Grissom, P. M., and McIntosh, J. R. (1985) Nature 318, 483-486). This partially purified kinesin is then adsorbed to a glass coverslip, mixed with microtubules and ATP, and viewed by video-enhanced differential interference contrast microscopy. The microtubule translocating activity of the purified egg kinesin is qualitatively similar to the analogous activity observed in crude extracts of sea urchin eggs and resembles the activity of neuronal kinesin with respect to both the maximal rate (greater than 0.5 micron/s) and the direction of movement. Axonemes glide on a kinesin-coated coverslip toward their minus ends, and kinesin-coated beads translocate toward the plus ends of centrosome microtubules. Sea urchin egg kinesin is inhibited by high concentrations of SH reagents ([N-ethylmaleimide] greater than 3-5 mM), vanadate greater than 50 microM, and [nonhydrolyzable nucleotides] greater than or equal to [MgATP]. The nucleotide requirement of sea urchin egg kinesin is fairly broad (ATP greater than GTP greater than ITP), and the rate of microtubule movement increases in a saturable fashion with the [ATP]. We conclude that the motile activity of egg kinesin is indistinguishable from that of neuronal kinesin. We propose that egg kinesin may be associated with microtubule-based motility in vivo.     

Pollination biology of the Proteaceae in Australia and southern Africa

Proteaceae are most diverse in southern Africa and Australia, especially in the south-western portions of these regions. Most genera have some species in flower at all times of the year, although generally there is a preponderance of species that flower between late winter and early summer. The one genus that is an exception to this generalization is Banksia, which either has approximately the same percentage of species in flower at various times of the year (southwestern Australia) or peaks in autumn (southeastern Australia). Within particular communities, opportunities for hybridization among congeneric species are minimized by staggered flowering times, different pollen vectors and/or various incompatibility mechanisms. Birds, mammals and arthropods have been identified as visitors to the inflorescences of many Proteaceae. The most common avian visitors to the majority of genera in Australia are honeyeaters, although lorikeets, silvereyes and approximately 40 other species sometimes may be important. Sugarbirds and sunbirds are seen most frequently at inflorescences of Protea, Leucospermum and Mimetes in southern Africa, although they rarely visit other genera. In most cases, avian visitors forage in a manner that permits the acquisition and transfer of pollen. Limited evidence supports the hypothesis that birds are selective in their choice of inflorescences, responding to morphological and/or colour changes and usually visiting those inflorescences that offer the greatest nectar rewards. Arthropods may be equally selective, although it is possible that only the larger moths, bees and beetles are important pollinators, even for those plant species that rely entirely on arthropods for pollen transfer. Mammals are pollen vectors for some Proteaceae, especially those that have geoflorous and/or cryptic inflorescences. In Australia, small marsupials may be the most important mammalian pollinators, although rodents fill this niche in at least some southern African habitats. All but two genera of Proteaceae are hermaphroditic and protandrous, the exceptions being the dioecious southern African genera Aulax and Leucadendron. For hermaphroditic species, the timing of visits by animals to inflorescences is such that they not only acquire pollen from freshly opened flowers but also brush against pollen presenters and stigmas of others that have lost self-pollen and become receptive. Birds and insects (and probably mammals) generally forage in such a way as to facilitate both outcrossing and selfing. Some species are self-compatible, although many require outcrossing if viable seed is to be formed. Regardless of which animals are the major pollen vectors, fruit set is low relative to the number of flowers available, especially in Australian habitats. Functional andromonoecy of the majority of flowers is advanced as the major cause of poor fruit set. The pollination biology and breeding systems of Australian and southern African Proteaceae resemble one another in many ways, partly because of their common ancestry, but also due to convergence. Divergence is less obvious, apart from the dichotomy between dioecious and hermaphroditic genera, and differences in the levels of seed set for Australian and African species. Future studies should concentrate on identifying the most important pollinators for various Proteaceae, the manner in which their visits are integrated with floral development and factors responsible for limiting fruit set.