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11.
Halipegus dubius Klein, 1905 is redescribed and illustrated from a Brazilian frog Leptodactylus ocellatus. The type-material of Halipegus genarchella (Travassos, Artigas & Pereira, 1928) and Halipegus parva (Travassos, Artigas & Pereira, 1928) are redescribed with original figures. New synonyms are proposed: Halipegus salmini Yamaguti, 1958 is considered a synonym of H. genarchella, H. tropicus (Manter, 1936) sensu Kloss (1966) of H. parva and Genarchella lenti Fábio, 1984 of H. overstreeti (Brooks, Mayes & Thorson, 1979) n. comb. 相似文献
12.
Hypoxanthine-guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8) is a purine salvage enzyme that catalyses the conversion of hypoxanthine and guanine to their respective mononucleotides. Partial deficiency of this enzyme can result in the overproduction of uric acid leading to a severe form of gout, whilst a virtual absence of HPRT activity causes the Lesch-Nyhan syndrome which is characterised by hyperuricaemia, mental retardation, choreoathetosis and compulsive self-mutilation. The HPRT-encoding gene is located on the X chromosome in the region q26–q27 and consists of nine exons and eight introns totalling 57 kb. This gene is transcribed to produce an mRNA of 1.6 kb, which contains a protein encoding region of 654 nucleotides. With the advent of increasingly refined techniques of molecular biology, it has been possible to study the HPRT gene of individuals with a deficiency in HPRT activity to determine the genetic basis of the enzyme deficiency. Many different mutations throughout the coding region have been described, but in the absence of precise information on the three-dimensional structure of the HPRT protein, it remains difficult to determine any consistent correlation between the structure and function of the enzyme. 相似文献
13.
Evolution of karyotypic abnormalities and C-MYC oncogene amplification in human colonic carcinoma cell lines 总被引:7,自引:0,他引:7
C. C. Lin Kari Alitalo Manfred Schwab Donna George Harold E. Varmus J. Michael Bishop 《Chromosoma》1985,92(1):11-15
Cell lines (COLO 320 DM and COLO 320 HSR), established from a human neuroendocrine tumor, contain an amplified cellular oncogene (c-myc). We have previously shown that the homogeneously staining regions (HSRs) of a marker chromosome in the COLO 320 HSR cells that evolved in culture from COLO 320 DM cells contain amplified c-myc. Molecular hybridization in situ has now been used to demonstrate that the HSRs are on both arms of what was once an X chromosome. We also show that amplified c-myc copies are present in the isolated double minute chromosomes (DMs) of the COLO 320 DM cells that were characteristic of the tumor cells initially established from the patient. The results suggest that the amplified c-myc appeared first as DMs and was subsequently transposed to engender HSRs on an X chromosome. The initial COLO 320 tumor cell may have acquired two early replicating (i.e., active) X chromosomes and lost the late replicating (i.e., inactive) X. 相似文献
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15.
Summary The lactose transport carrier from parental (X71/F'W3747) and mutant cells (54/F'5441) was reconstituted into proteoliposomes. Transport by the counterflow assay showed slightly greater activity in proteoliposomes prepared from extracts of the mutant membranes compared with that for the parental cell. The mutant carrier showed a threefold lowerK
m
but similarV
max compared to the parent. On the other hand proteoliposomes from the mutant showed a defect in protonmotive force-driven accumulation, compared with the parent. With a pH gradient (inside alkaline) plus a membrane potential (inside negative) the parental proteoliposomes accumulated lactose 25-fold over the medium concentration while the mutant proteoliposomes accumulated sixfold. In a series of experiments proteoliposomes were exposed to proteolytic enzymes. Chrymotrypsin treatment resulted in 30% inhibition of counterflow activity for the reconstituted carrier from both parent and mutant. Papain produced 84% inhibition of transport by the reconstituted parental carrier but only 41% of that of the mutant. Trypsin and carboxypeptidase Y treatment had no effect on counterflow activity of either parent or mutant. Exposure of purified lactose carrier in proteoliposomes to carboxypeptidase Y resulted in the release of alanine and valine, the two C-terminal amino acids predicted from the DNA sequence. 相似文献
16.
Renny T. Franceschi Hector F.De Luca Donna L. Mercado 《Archives of biochemistry and biophysics》1983,222(2):504-517
The interaction of the 1α,25-dihydroxyvitamin D3 receptor with immobilized calf thymus DNA has been compared with its sedimentation properties on hypotonic sucrose gradients. Forty to sixty percent of total hormone:receptor complexes formed at 4 °C were retained by DNA-cellulose and could be eluted by 0.18 to 0.2 m KCl. In contrast, heating preparations to 25 °C rapidly and irreversibly converted receptor to a form which bound hormone and DEAE-cellulose normally, but was unable to associate with DNA. Similarly, the ability of receptor to aggregate to a 6 S species was labile at 25 °C. Stabilization of receptor in the DNA binding aggregating form was accomplished using Ca2+, Mg2+, Mn2+, or Na2MoO4 while several protease and phosphatase inhibitors were ineffective. An examination of DNA binding properties of aggregating and nonaggregating receptor forms revealed that only receptor competent to enter into aggregates could bind DNA suggesting that a functional nucleic acid binding site, and, hence, a nucleic acid interaction is necessary for aggregate formation. Consistent with this view, an RNA:receptor interaction appears to be involved in formation of the 6 S complex since removal of RNA by ribonuclease treatment or purification of receptor reduced aggregation, an effect that could be reversed by addition of purified RNA. 相似文献
17.
Cytosol from rabbit heart and slow and fast skeletal muscles was fractionated using (NH4)2SO4 to yield three cytosolic protein fractions, viz., CPF-I (protein precipitated at 30% saturation), CPF-II (protein precipitated between 30 and 60% saturation), and cytosol supernatant (protein soluble at 60% saturation). The protein fractions were dialysed and tested for their effects on ATP-dependent, oxalate-supported Ca2+ uptake by sarcoplasmic reticulum from heart and slow and fast skeletal muscles. CPF-I from heart and slow muscle, but not from fast muscle, caused marked inhibition (up to 95%) of Ca2+ uptake by sarcoplasmic reticulum from heart and from slow and fast muscles. Neither unfractionated cytosol nor CPF-II or cytosol supernatant from any of the muscles altered the Ca2+ uptake activity of sarcoplasmic reticulum. Studies on the characteristics of inhibition of sarcoplasmic reticulum Ca2+ uptake by CPF-I (from heart and slow muscle) revealed the following: (a) Inhibition was concentration- and temperature-dependent (50% inhibition with approx. 80 to 100 μg CPF-I; seen only at temperatures above 20°C). (b) The inhibitor reduced the velocity of Ca2+ uptake without appreciably influencing the apparent affinity of the transport system for Ca2+. (c) Inhibition was uncompetitive with respect to ATP. (d) Sarcoplasmic reticulum washed following exposure to CPF-I showed reduced rates of Ca2+ uptake, indicating that inhibition results from an interaction of the inhibitor with the sarcoplasmic reticulum membrane. (e) Concomitant with the inhibition of Ca2+ uptake, CPF-I also inhibited the Ca2+-ATPase activity of sarcoplasmic reticulum. (f) Heat-treatment of CPF-I led to loss of inhibitor activity, whereas exposure to trypsin appeared to enhance its inhibitory effect. (g) Addition of CPF-I to Ca2+-preloaded sarcoplasmic reticulum vesicles did not promote Ca2+ release from the vesicles. These results demonstrate the presence of a soluble protein inhibitor of sarcoplasmic reticulum Ca2+ pump in heart and slow skeletal muscle but not in fast skeletal muscle. The characteristics of the inhibitor and its apparently selective distribution suggest a potentially important role for it in the in vivo regulation of sarcoplasmic reticulum Ca2+ pump, and therefore in determining the duration of Ca2+ signal in slow-contracting muscle fibers. 相似文献
18.
DIVISION IN THE DINOFLAGELLATE GYRODINIUM COHNII (SCHILLER) : A New Type of Nuclear Reproduction 总被引:10,自引:5,他引:5 下载免费PDF全文
Dinoflagellates are of interest because their chromosomes resemble the nucleoplasm of prokaryotes both chemically and ultrastructurally. We have studied nuclear division in the dinoflagellate Gyrodinium cohnii (Schiller), using cells obtained from cultures undergoing phasic growth. Electron micrographs of serial sections were used to prepare three-dimensional reconstructions of nuclei and chromosomes at various stages of nuclear division. During division, a complex process of invagination of the intact nuclear envelope takes place at one side of the nucleus and results in the formation of parallel cylindrical cytoplasmic channels through the nucleus. These invaginations contain bundles of microtubules, and each of the bundles comes to lie in the cytoplasm of a cylindrical channel. Nuclear constriction occurs perpendicular to these channels without displacement of the microtubules. There are no associations between chromosomes and the cytoplasmic microtubules. In dividing cells most chromosomes become V-shaped, and the apices of the V's make contact with the membrane surrounding cytoplasmic channels. It is proposed that the membrane surrounding cytoplasmic channels in the dividing nucleus may be involved in the separation of daughter chromosomes. Thus, dinoflagellates may resemble prokaryotes in the manner of genophore separation as well as in genophore chemistry and ultrastructure. 相似文献
19.
20.
Induction of c-fos mRNA Expression by Afterdischarge in the Hippocampus of Naive and Kindled Rats 总被引:5,自引:3,他引:2
Cheolsu Shin‡ James O. McNamara†‡ James I. Morgan§ Tom Curran Donna R. Cohen 《Journal of neurochemistry》1990,55(3):1050-1055
Periodic induction of focal electrical seizure [afterdischarge (AD)] is an absolute prerequisite for the development of kindling, an animal model of complex partial epilepsy. Once established, it is a permanent condition. The mechanism(s) that translate ADs, which last tens of seconds, into life-long alterations in the CNS is unclear. Cellular immediate-early genes have been implicated in the conversion of short-term stimuli to long-term alterations in cellular phenotypes by regulating target gene expression. We have investigated the contribution of one such early gene, c-fos, to this process. The relationship between ADs and expression of c-fos gene in the rat hippocampus, a key structure in kindling development, was studied by analysis of mRNA levels. The low constitutive expression of c-fos mRNA in the hippocampus was not altered by kindling. There was an "all-or-none" relationship between induction of c-fos and the duration of AD. The threshold for induction was approximately 30 s of AD. Above-threshold ADs induced c-fos in both naive and kindled animals to the same extent and with identical temporal profiles. Although the expression of c-fos is unchanged with kindling, c-fos may nonetheless contribute to many long-term changes of kindling, both adaptive and epileptogenic. 相似文献