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61.
Genetic studies have uncovered many genes that are involved in the first steps of neuronal development inDrosophila.Less is known about the intermediate steps during which individual precursor cells follow either the neuronal pathway or the glial pathway. We report the identification of a novel bHLH gene,biparous,expressed in neuronal and glial precursors inDrosophila.Unlike most bHLH genes,biparousexpression continues to the final stages of neurogenesis in the embryo. Expression ofbiparousis not observed in end stage postmitotic neurons and precedes the expression ofrepo,a gene activated in later stages of glial differentiation. The bHLH domain is sufficiently different from previously described bHLH domains to imply a novel function. 相似文献
62.
Amino acid sequence analysis has established that the homologous pairing protein of Ustilago maydis, known previously in the literature as rec1, is encoded by REC2, a gene essential for recombinational repair and meiosis with regional homology to Escherichia coli RecA. The 70-kDa rec1 protein is most likely a proteolytic degradation product of REC2, which has a predicted mass of 84 kDa but which runs anomalously during sodium dodecyl sulfate-gel electrophoresis with an apparent mass of 110 kDa. To facilitate purification of the protein product, the REC2 gene was overexpressed from a vector that fused a hexahistidine leader sequence onto the amino terminus, enabling isolation of the REC2 protein on an immobilized metal affinity column. The purified protein exhibits ATP-dependent DNA renaturation and DNA-dependent ATPase activities, which were reactions characteristic of the protein as purified from cell extracts of U. maydis. Homologous pairing activity was established in an assay that measures recognition via non-Watson-Crick bonds between identical DNA strands. A size threshold of about 50 bp was found to govern pairing between linear duplex molecules and homologous single-stranded circles. Joint molecule formation with duplex DNA well under the size threshold was efficiently catalyzed when one strand of the duplex was composed of RNA. Linear duplex molecules with hairpin caps also formed joint molecules when as few as three RNA residues were present. 相似文献
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A method was developed to predict spoilage of minced meat at chill temperatures, based on the difference in proton efflux from and influx into bacterial cells. This difference depends on the number of organisms present, the available glucose in the meat sample and the ability of the organisms to metabolize amino acids. The proton efflux/influx of a meat filtrate containing bacteria was measured at 25°C with a pH/ion meter in the presence of peptone with or without glucose. There was a noticeable rate of change of mV h-1 of the meat filtrate prior to the organoleptic detection of spoilage which may be used semi-predictively to determine the remaining shelf-life of meat at different storage temperatures. The method could be investigated further, encompassing type and relative numbers of organisms, incubation temperature, meat type and composition (i.e. available glucose) to produce a spoilage prediction model. The method does not require sophisticated equipment, only a standard pH/ion meter, is cheap, needing only peptone and glucose, is relatively simple, and takes less than 2 h to perform. 相似文献
67.
Twenty-five freshwater populations of Ceramiales were collected in North America, 24 of which were from the tropical rainforest region of Central America and the Caribbean. The streams tended to be moderate in mean current velocity (X?= 23.3 cm·S?1) and maximum width (X?= 6.3 m) but high in temperature (X?= 23.1°C), pH (X?= 7.9), and specific conductance (X?= 320 μS·cm?1). Three Bostrychia species were restricted to the Caribbean islands: B. moritziana (Sonder ex Kütz.) J. Ag. (syn. B. cornigera Mont. and B. radicans f. moliforme Post), with ecorticate indeterminate axes, monosiphonous ultimate branches, and cladohaptera; B. radicans (Mont.) Mont. (syn. B. leprieurii Mont and B. rivularis Harv.), with ecorticate and polysiphonous axes throughout and cladophaptera; and B. tenella (Lamour.) J. Ag., with corticate indeterminate axes, monosiphonous ultimate branches, and peripherohaptera. Ballia prieurii Kütz. was found in Belize and Costa Rica and was characterized by rebranched determinate laterals, opposite branching, and long apical cells (X?= 61 μm) and axial cells (X?= 43 μm). Caloglossa leprieurii (Mont.) J. Ag. was localized in Puerto Rico while. C. ogasawaerensis Okam. was collected only in Costa Rica. The two species were separated by site of branching (midrib vs. margin) and blade width (X?= 384 vs. 861 μm). Polysiphonia subtilissima Mont. from Florida and Jamaica had four pericentral cells, no cortication, rhizoids arising from pericentral cells, and branches initiated at trichoblast scars. 相似文献
68.
Use of an ordered cosmid library to deduce the genomic organization of Mycobacterium leprae 总被引:18,自引:4,他引:14
K. Eiglmeier N. Honoré S. A. Woods † B. Caudron S. T. Cole 《Molecular microbiology》1993,7(2):197-206
In an attempt to unify the genetic and biological research on Mycobacterium leprae, the aetiological agent of leprosy, a cosmid library was constructed and then ordered by a combination of fingerprinting and hybridization techniques. The genome of M. leprae is represented by four contigs of overlapping clones which, together, account for nearly 2.B Mb of DNA. Several arguments suggest that the gaps between the contigs are small in size and that virtually complete coverage of the chromosome has been obtained. All of the cloned M. leprae genes have been positioned on the contig maps together with the 29 copies of the dispersed repetitive element, RLEP. These have been classified into four groups on the basis of differences in their organization. Several key housekeeping genes were identified and mapped by hybridization with heterologous probes, and the current genome map of this uncultivable pathogen comprises 72 loci. 相似文献
69.
Twenty-seven populations of Tuomeya, including the types of Tuomeya fluviatilis Harvey and Baileya americana Kützing, were analyzed from the entire known range of the genus: northern Newfoundland to northern Florida and east of the Mississippi River. Key morphological features were examined in detail since it has been recently proposed that Tuomeya should be reduced to a section of the genus Batrachospermum. Our observations confirmed the presence of several characteristics unique to Tuomeya: gametophyte development from a basal mass of undifferentiated cells rather than a chantransia stage, pseudoparenchymatous growth, and carpogonia with obliquely to perpendicularly attached trichogynes. Based on these findings, we conclude that the genus Tuomeya should be retained. Using multivariate morphometrics, two groupings were found that differed significantly in plant length (X = 14.1 and 24.1 mm, respectively). However, since there was no other morphometric, environmental, or geographic basis for separation of the groupings, only one species is recognized, T. americana (Kützing) Papenfuss. Populations tend to occur in large streams (>2.8 m wide) with low ion content (≤ 100 μS · cm?1). 相似文献
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