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991.
Toe pad morphology and mechanisms of sticking in frogs 总被引:4,自引:0,他引:4
SHARON B. EMERSON DIANA DIEHL 《Biological journal of the Linnean Society. Linnean Society of London》1980,13(3):199-216
Sticking ability in frogs was measured on a series of different substrates. Analysis of performance suggests that frogs use two sticking mechanisms: interlocking on rough surfaces and capillarity on smooth surfaces. There is a correlation between morphological specializations of the toe pad and sticking ability, but these morphological features are not unique to arboreal species. Terrestrial species that use leaves as resting sites during times of inactivity have many of the same morphological specializations and stick as well as the strictly arboreal species. 相似文献
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Gene 32 protein (g32P), the single-stranded DNA binding protein from bacteriophage T4, contains 1 mol of Zn(II)/mol of protein. This intrinsic zinc is retained within the DNA-binding core fragment, g32P-(A+B) (residues 22-253), obtained by limited proteolysis of the intact protein. Ultraviolet circular dichroism provides evidence that Zn(II) binding causes significant changes in the conformation of the peptide chain coupled with alterations in the microenvironments of tryptophan and tyrosine side chains. NMR spectroscopy of the 113Cd(II) derivative of g32P-(A+B) at both 44.4 and 110.9 MHz shows a single 113Cd resonance, delta 637, a chemical shift consistent with coordination to three of the four sulfhydryl groups in the protein. In vitro mutagenesis of Cys166 to Ser166 creates a mutant g32P that still contains 1 Zn(II)/molecule. This mutant protein when substituted with 113Cd(II) shows a 113Cd signal with a delta and a line width the same as those observed for the wild-type protein. Thus, the S-ligands to the metal ion appear to be contributed by Cys77, Cys87, and Cys90. Relaxation data suggest that chemical shift anisotropy is the dominant, but not exclusive, mechanism of relaxation of the 113Cd nucleus in g32P, since a dipolar modulation from ligand protons is observed at 44.4 MHz but not at 110.9 MHz. Complexation of core 113Cd g32P with d(pA)6 or Co(II) g32P with poly(dT) shows only minor perturbation of the NMR signal or d-d electronic transitions, respectively, suggesting that the metal ion in g32P does not add a ligand from the bound DNA.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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K B Choo K Y Chong H F Chou L N Liew C C Liou 《Biochemical and biophysical research communications》1989,158(1):334-340
The structure of the c-myc oncogene in 17 cervical tumors and patient-matched nontumor tissues from Chinese patients residing in Taiwan was analysed. In contrast to recent reports on Mexican patients, none of the samples showed rearrangements and sequence amplification in the c-myc gene. The discrepancy may be explained by different carcinogenesis mechanisms being in operation in different geographic regions. Although no structural alterations in the c-myc gene were found in seven cervical carcinoma cell lines analysed, Northern blot analysis indicated different levels of c-myc gene expression which may be related to the presence of human papillomavirus (HPV) sequence in the cell and suggests a possible c-myc-hpv interaction in some stages of the transformation process. 相似文献