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21.
Conformational studies have been carried out on hydrogenbonded all-trans cyclic pentapeptide backbone. Application of a combination
of grid search and energy minimization on this system has resulted in obtaining 23 minimum energy conformations, which are
characterized by unique patterns of hydrogen bonding comprising of β- and γ-turns. A study of the minimum energy conformationsvis-a-vis non-planar deviation of the peptide units reveals that non-planarity is an inherent feature in many cases. A study on conformational
clustering of minimum energy conformations shows that the minimum energy conformations fall into 6 distinct conformational
families. Preliminary comparison with available X-ray structures of cyclic pentapeptide indicates that only some of the minimum
energy conformations have formed crystal structures. The set of minimum energy conformations worked out in the present study
can form a consolidated database of prototypes for hydrogen bonded backbone and be useful for modelling cyclic pentapeptides
both synthetic and bioactive in nature.
This is part XV of the series. Part XIV in this series is Ramakrishnanet al 1987. 相似文献
22.
Regulation of the mouse sex-limited protein (Slp) gene is unusual in that hormone response is conferred by the 5′ LTR of an upstream inserted provirus, dubbed the imposon
(imp1). In a search for additional genes whose regulation has been affected by retrotransposition events, we isolated two partial
proviral elements by stringent screening of a mouse genomic library. One clone (imp2) contained a portion of the envelope gene and a 3′ LTR that was nearly identical to the 3′ LTR of imp1; this similarity extended to insertion into a B1 repetitive element. The second proviral clone (imp3) contained a 5′ LTR and associated coding sequences, but lacked its 3′ LTR; the LTR of imp3 differed by 12% from the imp1 sequence. To assess potential hormone response, proviral enhancer regions cloned into reporter vectors were tested in transfection.
The imp2 enhancer was similar in behavior to imp1, conferring both androgen and glucocorticoid induction in one fragment context and an androgen-specific response in another.
In contrast, the imp3 enhancer allowed high expression in the absence of hormone and was less responsive to steroids in general and androgen in
particular. These three proviral elements define a small family of steroid responsive proviruses in the mouse genome, and
at least one member has had a lasting impact on an endogenous gene's regulation.
Received: 29 April 1997 / Accepted: 14 July 1997 相似文献
23.
24.
R Sowdhamini N Srinivasan C Ramakrishnan P Balaram 《Journal of molecular biology》1992,223(4):845-851
A super-secondary structural motif comprising two orthogonally oriented beta-strands connected by short linking segments of less than or equal to 5 residues has been identified from a data set of 65 independent protein crystal structures. Of the 42 examples from 14 proteins, a vast majority have only a single residue as the linking element. Analysis of the conformational angles at the junction reveals that the recently described type VIII beta-turn occurs frequently at the connecting hinge, while the type II beta-turn is also fairly common. 相似文献
25.
Studies were made of the effects of maternal thiamine deficiency on rat whole brain, gray matter and white matter lipids. Mothers were fed a high protein diet (controls) or thiamine deficient high protein diet (thiamine deficient, TD) from 14th day of gestation through lactation. An additional group (pair fed control, PFC) was pair fed with the thiamine deficient group. The TD pups started showing symptoms of abnormalities in posture, arched back and hind limb paralysis from 16th day of lactation. Significant deficits were found in body weight and brain weight of TD and PFC pups. But the deficits seem to be more in the former group. Significant deficits were observed with regard to the concentration of lipids such as galactolipids, phospholipids and plasmalogens in the whole brain of TD and PFC pups at 21 days of age. Additional deficits were also found in the concentration of cholesterol in PFC pups. Gray matter lipids from TD pups seem to be completely spared. However, deficits were found in galactolipid and ganglioside concentrations in PFC pups. The deficits found in the concentration of different lipids in white matter are similar to those observed in whole brain. These results suggest that the effects of thiamine deficiency may be partly due to resultant growth retardation and partly due to the deficiency of thiamine per se. 相似文献
26.
V.R. Ramakrishnan S. Yabuki I.-Y. Sillers D.G. Schindler D.M. Engelman P.B. Moore 《Journal of molecular biology》1981,153(3):739-760
A map of the positions of 12 of the 21 proteins of the 30 S ribosomal subunit of Escherichia coli (S1, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12 and S15), based on neutron scattering, is presented and discussed. Estimates for the radii of gyration of these proteins in situ are also obtained. It appears that many ribosomal proteins have compact configurations in the particle. 相似文献
27.
28.
P. K. Asha M. S. Shaila C. S. Vaidyanathan T. Ramakrishnan 《Journal of biosciences》1979,1(3):327-334
Treatment ofTrigonella foenumgraeceum (fenugreek) seedlings with naphthalene acetic acid plus gibberellic acid enhanced the RNA synthesising capacity of nuclei
isolated from the hypocotyl and cotyledonary regions. This increase was more pronounced in the nuclei from the hypocotyl region
than from the cotyledonary region.In vitro addition of these phytohormones did not stimulate RNA synthesis by nuclei. The RNA synthesis by mitochondria was not affected
by preincubating the seedlings with the hormones. The nuclei isolated from callus cultures of fenugreek hypocotyl treated
with the hormone also showed increased RNA synthesis. 相似文献
29.
30.
The isolation and structure determination of a glycosidic germacradienolide from Eupatorium altissimum are reported. Eupatorin and 5-hydroxy-3′,4′,6,7-tetramethoxyflavone were also found. 相似文献