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73.
Background
Cyclic nucleotides are ubiquitous intracellular messengers. Until recently, the roles of cyclic nucleotides in plant cells have proven difficult to uncover. With an understanding of the protein domains which can bind cyclic nucleotides (CNB and GAF domains) we scanned the completed genomes of the higher plants Arabidopsis thaliana (mustard weed) and Oryza sativa (rice) for the effectors of these signalling molecules. 相似文献74.
75.
Extremity reconstruction using the free deltoid flap 总被引:2,自引:0,他引:2
The deltoid fasciocutaneous flap is a thin, reliable flap that is easily dissected from the posterolateral arm. It has large-caliber vessels and is capable of sensory reinnervation to portions of the flap above the deltoid/triceps groove through the lateral brachial cutaneous nerve. There is little sensory return to the large vascular territory, which can be extended inferiorly below the deltoid triceps groove. The donor site can be closed primarily or skin grafted and when large may be objectionable to some patients. The flap is an excellent choice for extremity soft-tissue reconstruction on the plantar or palmar surfaces. Protective sensibility has returned to all reinnervated flaps. We present our experience in 10 patients with extremity problems. 相似文献
76.
Determining the evolutionary potential of a gene 总被引:4,自引:0,他引:4
In addition to information for current functions, the sequence of a gene
includes potential information for the evolution of new functions. The
wild-type ebgA (evolved beta-galactosidase) gene of Escherichia coli
encodes a virtually inactive beta-galactosidase, but that gene has the
potential to evolve sufficient activity to replace the lacZ gene for growth
on the beta-galactoside sugars lactose and lactulose. Experimental
evidence, which has suggested that the evolutionary potential of Ebg enzyme
is limited o two specific amino acid replacements, is limited to examining
the consequences of single base- substitutions. Thirteen
beta-galactosidases homologous with the Ebg beta-galactosidase are widely
dispersed, being found in gram-negative and gram-positive eubacteria and in
a eukaryote. A comparison of Ebg beta-galactosidase with those 13
beta-galactosidases shows that Ebg is part of an ancient clade that
diverged from the paralogous lacZ beta- galactosidase over 2 billion years
ago. Ebg differs from other members of its clade at only 2 of the 15
active-site residues, and the two mutations required for full Ebg
beta-galactosidase activity bring Ebg into conformity with the other
members of its clade. We conclude that either these are the only acceptable
amino acids at those positions, or all of the single-base-substitution
replacements that must arise as intermediates on the way to other
acceptable amino acids are so deleterious that they constitute a deep
selective valley that has not been traversed in over 2 billion years. The
evolutionary potential of Ebg is thus limited to those two replacements.
相似文献
77.
Differential grazing on protozoan microplankton by developmental stages of the calanoid copepod Eurytemora affinis Poppe 总被引:5,自引:0,他引:5
Nauplii and adults of the copepod Eurytemora affinis Poppe collectedfrom the Multiscale Experimental Ecosystem Research Center (MEERC)mesocosms and from the Choptank River (a subestuary of ChesapeakeBay) reduced ciliate and dinoflagellate microplankton densitiessignificantly during grazing experiments. Protozoan microplanktongenerally were consumed in proportion to their availability,although both adult copepod and naupliar clearance rates werehigher for larger prey ({small tilde}40µm). Ingestionof ciliate microplankton was confirmed by examining copepodgut fluorescence after brief (1 h) incubations with ciliateslabeled with a fluorescent vital stain (5-chloromethylfluoresceindiacetate). In addition, both adults and nauplii of E.affiniscleared protozoan microplankton at considerably higher ratesthan chlorophyll a. Naupliar clearance rates were generallyan order of magnitude lower than adult rates, but given naupliarabundances in copepod assemblages, they should contribute substantiallyto total grazing on protozoan microplankton. Grazing by thetotal copepod assemblage in mesocosms and in the field may beunderestimated if juvenile stages are ignored. 相似文献
78.
K J Riggs S Saleque K K Wong K T Merrell J S Lee Y Shi K Calame 《Molecular and cellular biology》1993,13(12):7487-7495
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80.