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11.
We examined the codon usages in well-conserved and less-well-conserved regions of vertebrate protein genes and found them to be similar. Despite this similarity, there is a statistically significant decrease in codon bias in the less-well-conserved regions. Our analysis suggests that although those codon changes initially fixed under amino acid replacements tend to follow the overall codon usage pattern, they also reduce the bias in codon usage. This decrease in codon bias leads one to predict that the rate of change of synonymous codons should be greater in those regions that are less well conserved at the amino acid level than in the better-conserved regions. Our analysis supports this prediction. Furthermore, we demonstrate a significantly elevated rate of change of synonymous codons among the adjacent codons 5' to amino acid replacement positions. This provides further support for the idea that there are contextual constraints on the choice of synonymous codons in eukaryotes. 相似文献
12.
Roni J. Kingsley Asenath M. Bernhardt Karl M. Wilbur Norimitsu Watabe 《In vitro cellular & developmental biology. Plant》1987,23(4):297-302
Summary Scleroblasts were separated from fragmented tissue of growing tips ofLeptogorgia virgulata and cultured using a modification of the technique of Rannou. Replacement of fetal bovine serum with horse serum seemed to
increase scleroblast viability. Cell adhesion occurred from 14 to 43 d. Cultured scleroblasts demonstrated cell aggregation,
spicule formation, and extrusion of spicules into the external medium. Cells showing spicules in the process of being extruded
appeared on the average after 24 d of culture. Variability among cultures was marked with respect to both division and spicule
formation. Healthy cultures were maintained for more than 4 mo.
This work was supported by National Science Foundation grants PCM8201389 and DCB8502698. This is contribution No. 674 of Belle
W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina. 相似文献
13.
Charles Romeo Naoko Moriwaki Kerry T. Yasunobu Irwin C. Gunsalus Hideo Koga 《The protein journal》1987,6(3):253-261
The first 12 NH2-terminal amino acids of the Pseudomonas putida putidaredoxin reductase were shown to be Met-Asn-Ala-Asn-Asp-Asn-Val-Val-Ile-Val-Gly-Thr. Comparison of these data with the DNA sequence of the BamHI-HindIII 197-base fragment derived from the PstI 2.2-kb fragment obtained from the P. putida plasmid showed that the putidaredoxin reductase gene was downstream from the cytochrome P-450 gene and the intergenic region had the 24-nucleotide sequence TAAACACATGGGAGTGCGTGCTAA. The Shine-Dalgarno sequence GGAG was detected in this region. The initiating triplet for the reductase gene was GTG, which normally codes for valine, but in the initiating codon position codes for methionine. From the amino acid sequence and X-ray data comparisons with other flavoproteins, what appears to be the AMP binding region of the FAD can be recognized in the NH2-terminal portion of the reductase involving residues 5–35. 相似文献
14.
We have studied the statistical constraints on synonymous codon choice to evaluate various proposals regarding the origin of the bias in synonymous codon usage observed by Fiers et al. (1975), Air et al. (1976), Grantham et al. (1980) and others. We have determined the statistical dependence of the degenerate third base on either of its nearest neighbors in mitochondrial, prokaryotic, and eukaryotic coding sequences. We noted an increasing dependence of the third base on its nearest neighbors in moving from mitochrondria to prokaryotes to eukaryotes.A statistical model assuming random equiprobable selection of synonymous codons was found grossly adequate for the mitochondria, but totally indequate for prokaryotes and eukaryotes. A model assuming selection of synonymous codons reflecting a genomic strategy, i.e. the genome hypothesis of Grantham et al. (1980), gave a good approximation of the mitochondrial sequences. A statistical model which exactly maintains codon frequency, but allows the position of corresponding synonymous codons to vary was only grossly adequate for prokaryotes and totally inadequate for eukaryotes. The results of these simulations are consistent with the measures on experimental sequences and suggest that a “frequency constraint” model such as that of Grantham et al. (1980) may be an adequate explanation of the codon usage in mitochondria. However, in addition to this frequency constraint, there may be constraints on synonymous codon choice in prokaryotes due to codon context. Furthermore, any proposal to explain codon usage in eukaryotes must involve a constraint on the context of a codon in the sequence. 相似文献
15.
Isolation, Mapping, and Characterization of Trehalaseless Mutants of Neurospora crassa 总被引:4,自引:0,他引:4 下载免费PDF全文
Alfred S. Sussman M. Kerry Garrett Malcolm Sargent Shih-An Yu 《Journal of bacteriology》1971,108(1):59-68
Mutant strains of Neurospora crassa that lack trehalase and are unable to grow on trehalose were isolated, and the gene (tre) was positioned on the right arm of linkage group I. Maltase and beta-galactosidase activities are almost identical in tre(-) strains, whereas that of invertase was reduced by more than half and those of acid phosphatase and amylase were somewhat increased. Heterocaryons between standard and trehalaseless strains yield less than one-tenth the activity of the former. In addition, strains with duplications heterozygous for trehalase produce less than 1% of the activity of the standard strain. An inhibitor of trehalase has been found in tre(-) strains; its sensitivity to heat and proteolysis, and its nondialyzability suggest that this substance is a protein. The mig gene, which determines the rate of migration of trehalase on acrylamide gels, has been shown to be less than 1 map unit away from the tre gene. 相似文献
16.
Robert L. Wilbur 《Brittonia》1969,21(4):355-358
A newCentropogon (sect.Wimmeriopsis subsect.Colombiani) from the Cordillera de Talamanca, Costa Rica, is described and compared toC. gutierrezii (Planch. & Oerst.) F. E. Wimmer, a species restricted to the Cordillera Central with which it previously has been confused. 相似文献
17.
STUDIES ON SHELL FORMATION : IX. An Electron Microscope Study of Crystal Layer Formation in the Oyster 总被引:3,自引:2,他引:1 下载免费PDF全文
Details of crystal growth in the calcitostracum of Crassostrea virginica have been studied with the purpose of analyzing the formation of the overlapping rows of oriented tabular crystals characteristic of this part of the shell. Crystal elongation, orientation, and dendritic growth suggest the presence of strong concentration gradients in a thin layer of solution in which crystallization occurs. Formation of the overlapping rows can be explained by three processes observed in the shell: a two-dimensional tree-like dendritic growth in which one set of crystal branchings creeps over an adjacent set of branchings; three-dimensional dendritic growth; and growth by dislocation of crystal surfaces. Multilayers of crystals may thus be formed at one time. This is favored by infrequent secretion of a covering organic matrix which would inhibit crystal growth. The transitional zone covering the outer part of the calcitostracum and the inner part of the prismatic region is generally characterized by aggregates of small crystals with definite orientation. Growth in this zone appears to take place in a relatively homogeneous state of solution without strong concentration gradients. Thin membranes and bands of organic matrix were commonly observed in the transitional zone bordering the prismatic region. The membrane showed a very fine oriented network pattern. 相似文献
18.
H. L. Sudan C. J. Kerry I. R. Mellor S. -K. Choi D. Huang K. Nakanishi P. N. R. Usherwood 《Invertebrate neuroscience : IN》1995,1(2):159-172
The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin
on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory
postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR).
Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl
moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at
the distal end of the toxin molecule were generally 2–3 fold less potent than PhTX-343. When these compounds were tested in
subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V.
during application of photolabile toxin combined with either neural stimulation of the muscle orl-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible. 相似文献
19.
20.
Daphnopsis filipedunculata, a new species from Serra dos Carajás, Pará, Brazil, is distinguished by its long, thin primary peduncles and constricted hypanthium. 相似文献