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81.
The localization of specific human ubiquitin genes has not been straightforward because of the conservation of the ubiquitin coding sequence and the number of processed pseudogenes. An congruent to 1.4-kb sequence from the 5'-flanking region of the UBC gene has been shown to be unique to that locus and free from dispersed repeat elements. The cloned 5'-flanking fragment has been used to probe Southern blots of DNA obtained from somatic cell hybrid cell lines. These data indicate that the UBC gene is located on chromosome 12. In situ hybridization with the 5'-flanking probe has refined the assignment to the broad chromosomal subband 12q24.3. These data show that the active ubiquitin genes are not clustered and are located on separate chromosomes. In addition, these studies demonstrate the utility of intron or flanking sequence probes in the specific chromosomal assignment of members of highly conserved gene families. 相似文献
82.
The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level. 相似文献
83.
The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone 总被引:30,自引:1,他引:29
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The basis of inhibition of photosynthesis by single acute O3 exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O3 for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO2 uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO2 uptake and the internal CO2 concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O3; no significant increase occurred for any of the other treatments. Analysis of the response of CO2 uptake to the internal CO2 concentration implied that the predominant factor responsible for the reduction in light-saturated CO2 uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O3, respectively. At saturating concentrations of CO2, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O3. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO2 uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O3, requiring 8 hours at 400 nanomoles per mole O3 before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO2 uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O3 fumigation. 相似文献
84.
Role of neurogenic genes in establishment of follicle cell fate and oocyte polarity during oogenesis in Drosophila 总被引:16,自引:0,他引:16
Oogenesis in Drosophila involves specification of both germ cells and the surrounding somatic follicle cells, as well as the determination of oocyte polarity. We found that two neurogenic genes, Notch and Delta, are required in oogenesis. These genes encode membrane proteins with epidermal growth factor repeats and are essential in the decision of an embryonic ectodermal cell to take on the fate of neuroblast or epidermoblast. In oogenesis, mutation in either gene leads to an excess of posterior follicle cells, a cell fate change reminiscent of the hyperplasia of neuroblasts seen in neurogenic mutant embryos. Furthermore, the Notch mutation in somatic cells causes mislocalization of bicoid in the oocyte. These results suggest that the neurogenic genes Notch and Delta are involved in both follicle cell development and the establishment of anterior-posterior polarity in the oocyte. 相似文献
85.
MuB protein allosterically activates strand transfer by the transposase of phage Mu. 总被引:7,自引:0,他引:7
The MuA and MuB proteins collaborate to mediate efficient transposition of the phage Mu genome into many DNA target sites. MuA (the transposase) carries out all the DNA cleavage and joining steps. MuB stimulates strand transfer by activating the MuA-donor DNA complex through direct protein-protein contact. The C-terminal domain of MuA is required for this MuA-MuB interaction. Activation of strand transfer occurs irrespective of whether MuB is bound to target DNA. When high levels of MuA generate a pool of free MuB (not bound to DNA) or when chemical modification of MuB impairs its ability to bind DNA, MuB still stimulates strand transfer. However, under these conditions, intramolecular target sites are used exclusively because of their close proximity to the MuA-MuB-donor DNA complex. 相似文献
86.
Shyam K. Sharan Bernadette Holdener-Kenny David W. Threadgill Terry Magnuson 《Mammalian genome》1992,3(2):79-83
Sensitive methods for analysis of DNA from limited amounts of tissue are often difficult, error prone, and time consuming. Here, we describe a procedure for molecular analysis of individual early post-implantation mouse embryos by Southern analysis. The procedure involves embedding single embryos in agarose before lysing and deproteinizing in situ. The embedded DNA can be digested with restriction enzymes and analyzed by standard Southern-blotting procedures. The procedure is sensitive enough to detect single-copy sequences in embryos as early as day 6.5 of development. We have used the technique to genotype embryos homozygous for an embryonic lethal deletion. Normally, the lethal phenotype associated with such mutations is identified by a retrospective statistical analysis of abnormal embryos produced from a heterozygous cross as compared to those produced from a control cross. Now, if associated with a detectable DNA abnormality, the mutant embryo can be genotyped directly. We also report the use of this method for mapping cloned markers relative to deletion breakpoints. This approach can save considerable time since mapping would conventionally be done using restriction fragment length polymorphisms (RFLPs) detected in Mus musculus/Mus spretus interspecies hybrids. Using this procedure, we have been able to redefine the distal limits of the region of Chromosome (Chr) 7 containing a gene (eed) needed for development of the embryonic ectoderm. 相似文献
87.
Eugene M. Rinchik Terry Magnuson Bernadette Holdener-Kenny Gavin Kelsey Albert Bianchi Claudio J. Conti Fran?ois Chartier Kathryn A. Brown Stephen D. M. Brown Josephine Peters 《Mammalian genome》1992,3(Z1):S104-S120
Chair of Committee for Mouse Chromosome 7 相似文献
88.
Membrane transport proteins: implications of sequence comparisons. 总被引:27,自引:0,他引:27
J K Griffith M E Baker D A Rouch M G Page R A Skurray I T Paulsen K F Chater S A Baldwin P J Henderson 《Current opinion in cell biology》1992,4(4):684-695
Analyses of the sequences and structures of many transport proteins that differ in substrate specificity, direction of transport and mechanism of transport suggest that they form a family of related proteins. Their sequence similarities imply a common mechanism of action. This hypothesis provides an objective basis for examining their mechanisms of action and relationships to other transporters. 相似文献
89.
François Baneyx Amanda Ayling Terry Palumbo Daniel Thomas George Georgiou 《Applied microbiology and biotechnology》1991,36(1):14-20
Summary The expression of many secreted recombinant proteins in Gram-negative bacteria is limited by degradation in the periplasmic space. We have previously shown that the production of protein A--lactamase, a secreted fusion protein highly sensitive to proteolysis in Escherichia coli, can be increased in mutant strains deficient in up to three cell-envelope-associated proteolytic activities. In this work we investigated the effect of fermentation conditions on suppressing any residual proteolytic activity in various protease-deficient strains. Optimal production of the fusion protein was observed in cells grown under mildly acidic conditions (5.5pH6.0) and at low temperatures. These conditios were shown to specifically decrease the rate of proteolysis. In addition, a further increase in production was observed in cultures supplemented with 0.5 to 0.75 mM zinc chloride. This may relate to the inhibition of a cell envelope protease by Zn2+ ions.
Offsprint requests to: G. Georgiou 相似文献
90.
Terry B. White Dianne K. Hammond Hernán Vásquez Henry W. Strobel 《Molecular and cellular biochemistry》1991,102(1):61-69
Cytochrome P450 is known to cause carcinogen activation and correspondingly increased cancer risk in animal models. In order to determine whether P450 in the colon may be involved in cancer development in the human, the human colon cell line LS174T was examined for the presence of various cytochromes P450. Two isozymes of P450 were identified in the human cell line. Expression of P450IAl or IA2 was increased by treatment of the cell line with benzanthracene; the induction was demonstrated by an increase in RNA hybridizing to a probe for P4501Al and by ethoxyresorufin deethylation activity. Western analysis of microsomes isolated from human colon tissue also demonstrated the presence of P4501A1, as well as a form which cross-reacted to an antibody to human P450IIC9. Another isozyme, P450IIE1, was identified by polymerase chain reaction amplification of RNA from LS174T cells. These results underscore the presence of cytochromes P450 in colonic tissue and provide a basis for the involvement of isozyme-specific P450 mediated reactions in carcinogenesis of the colon.Some of the data presented here were taken from a thesis submitted by D.K.H. in partial fulfillment of the requirements for the Ph.D. degree in the University of Texas Graduate School of Biomedical Sciences. 相似文献