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151.
C. D. Reymond P. Schaap M. Véron J. G. Williams 《Cellular and molecular life sciences : CMLS》1995,51(12):1166-1174
cAMP plays an essential role duringDictyostelium development both outside and inside the cell. Membrane-bound receptors and adenylyl cyclase are responsible for sensing and producing extracellular cAMP, whereas a phosphodiesterase is responsible for maintaining a low basal level. The molecular events underlying this type of hormone like signalling, which are now beginning to be deciphered, will be presented, in the light of cAMP analogue studies. The importance of intracellular cAMP for cell differentiation has been demonstrated by the central role of the cAMP dependent protein kinase. Mutants as well as strains obtained by reverse genetics will be reviewed which lead to our current understanding of the role of intracellular cAMP in the differentiation of both stalk and spore cells. 相似文献
152.
目前,由CO、CO_2和H_3合成甲醇反应的模式尚未能得出一致的观点。分歧主要在于合成过程中CO_2的作用。至七十年代中期,看法较为一致的模式为近年来,苏联学者采用动力学实验法和同位索示踪原子法对苏产CHM-1铜基催化剂进行研究,提出了另一种模式因而,为阐明甲醇合成反应模式,就必须阐明究竟甲醇是由CO、还是由CO_2 直接生成的。这不仅对于甲醇合成过程的优化,而且也对含CO_2工业废气的综合利用都是有意义的。本文在对国产C_(301)(Cu,ZnO和Al_2O_3组成)铜基催化剂进行动力学考察的基础上,研究CO_2在合成甲醇反应过程中的作用。实验压力5MP3,温度218—260℃,接触时间0.16—3.5秒,分别对仅含CO_2或CO和含CO、CO_2三种起始反应混合物气体进行了合成甲醇反应动力学行为的实验测定。结果表明:反应是一复杂的过程。对于含CO_2、H_2、Ar的混合物,由CO_2可以直接合成甲醇, 对含CO、H_2和Ar的混合物,甲醇由CO直接合成;而对既含CO_2又含CO 的混合物,甲醇同时由CO和CO_2合成。 相似文献
153.
Cloning of decay-accelerating factor suggests novel use of splicing to generate two proteins 总被引:9,自引:0,他引:9
Decay-accelerating factor (DAF), a glycoprotein that is anchored to the cell membrane by phosphatidylinositol, binds activated complement fragments C3b and C4b, thereby inhibiting amplification of the complement cascade on host cell membranes. Here, we report the molecular cloning of human DAF from HeLa cells. Analysis of DAF complementary DNAs revealed two classes of DAF messenger RNA, one apparently derived from the other by a splicing event that causes a coding frameshift near the C terminus. The apparent 'intron' sequence contains an Alu family member and encodes contiguous protein sequence. Two DAF proteins are therefore possible, having divergent C-terminal domains which differ in their hydrophobicity. Both mRNAs are found on polysomes, suggesting that both are translated. We propose that the major (90%) spliced DAF mRNA encodes membrane-bound DAF whereas the minor (10%) unspliced DAF mRNA may encode secreted DAF and we present expression data supporting this. The deduced DAF sequence contains four repeating units homologous to a consensus repeat found in a recently described family of complement proteins. 相似文献
154.
W F Bodmer C J Bailey J Bodmer H J Bussey A Ellis P Gorman F C Lucibello V A Murday S H Rider P Scambler 《Nature》1987,328(6131):614-616
Colorectal cancer is the second most common cancer in the United Kingdom and other developed countries in the West. Although it is usually not familial, there is a rare dominantly inherited susceptibility to colon cancer, familial adenomatous polyposis (FAP; also often previously called familial polyposis coli). During adolescence affected individuals develop from a few hundred to over a thousand adenomatous polyps in their large bowel. These are sufficiently likely to give rise to adenocarcinomas to make prophylactic removal of the colon usual in diagnosed FAP individuals. Adenomas may occur elsewhere in the gastrointestinal tract and the condition is often associated with other extracolonic lesions, such as epidermoid cysts, jaw osteomata and fibrous desmoid tumours. Adenomata have been suggested to be precancerous states for most colorectal tumours. Knudson has suggested that the mutation for a dominantly inherited cancer susceptibility may be the first step in a recessive change in the tumour cells, and that the same gene may be involved in both familial and non-familial cases of a given tumour. Following up a case report of an interstitial deletion of chromosome 5 in a mentally retarded individual with multiple developmental abnormalities and FAP, we have now shown that the FAP gene is on chromosome 5, most probably near bands 5q21-q22. 相似文献
155.
Kinetics of smooth and skeletal muscle activation by laser pulse photolysis of caged inositol 1,4,5-trisphosphate 总被引:1,自引:0,他引:1
Inositol 1,4,5-trisphosphate (InsP3) can stimulate skinned smooth and skeletal muscle to contract by initiating Ca2+ release from the sarcoplasmic reticulum. Whether this process is an integral component of the in vivo muscle activation mechanism was tested by releasing InsP3 rapidly within skinned muscle fibers of rabbit main pulmonary artery and frog semitendinosus. InsP3 was liberated on laser pulse photolysis of a photolabile but biologically inactive precursor of InsP3 termed caged InsP3. Caged InsP3 is a mixture of compounds in which InsP3 is esterified with 1(2-nitrophenyl)diazoethane (probably at the P4- or P5-position). Photochemical release of InsP3 induced a full contraction in both muscles at physiological free Mg2+ concentrations, but only in the smooth muscle were the InsP3 concentration (0.5 microM) and the activation rate compatible with the in vivo physiological response. Endogenous InsP3-specific phosphatase activity was present in smooth muscle and had about 35-fold greater activity than that in the skeletal-muscle preparation. Caged InsP3 was not susceptible to phosphatases in either preparation. 相似文献
156.
Leers MP Björklund V Björklund B Jörnvall H Nap M 《Cellular and molecular life sciences : CMLS》2002,59(8):1358-1365
We investigated the distribution and fate of apoptotic bodies during human development and in the adult, using an antibody
(M30) that recognizes a neo-epitope formed early in the apoptotic cascade by caspase cleavage of cytokeratin 18. In the fetus,
we found extensive accumulation of M30-positive, non-phagocytosed fragments in the red pulp of the spleen, subcutaneous and
submucosal vessels, the interstitium of the lung, and the glomerular mesangium of the kidneys. In the liver, M30-immunoreactive
fragments were found inside macrophages in the sinusoids. The number of these fragments and the intensity of the immunostaining
increased with the gestational age of the fetus. In the adult, M30-positive fragments were barely detectable in normal tissues.
However, many pathological situations, including both chronic degenerative processes and metastatic cancer, were associated
with accumulation of M30-positive fragments in the red pulp of the spleen. In the liver and kidney, no fragments could be
detected. Remarkably, 13 of the 16 patients with metastasized cancer showed pronounced accumulation of M30-positive fragments
containing hematoxylin-reactive material in the red pulp of the spleen. In the non-cancerous cases, such DNA-containing fragments
were only seen in 9 of 94 cases. The results show that when apoptotic activity is high, as during development in the fetus
or during metastasis and other pathological processes in the adult, the phagocytic clearance of apoptotic bodies can be overloaded.
These apoptotic fragments then accumulate in the spleen. The visual detection of apoptotic fragments is concluded to reflect
increased cell turnover.
Received 1 July 2002; accepted 1 July 2002 相似文献
157.
Screening for differentially expressed genes is a straightforward approach to study the molecular basis for changes in gene
expression. Differential display analysis has been used by investigators in diverse fields of research since it was developed.
Differential display has also been the approach of choice to investigate changes in gene expression in response to various
biological challenges in invertebrates. We review the application of differential display analysis of gene expression in invertebrates,
and provide a specific example using this technique for novel gene discovery in the nematode Caenorhabditis elegans. 相似文献
158.
Analysis of the mouse transcriptome based on functional annotation of 60,770 full-length cDNAs 总被引:6,自引:0,他引:6
Okazaki Y Furuno M Kasukawa T Adachi J Bono H Kondo S Nikaido I Osato N Saito R Suzuki H Yamanaka I Kiyosawa H Yagi K Tomaru Y Hasegawa Y Nogami A Schönbach C Gojobori T Baldarelli R Hill DP Bult C Hume DA Quackenbush J Schriml LM Kanapin A Matsuda H Batalov S Beisel KW Blake JA Bradt D Brusic V Chothia C Corbani LE Cousins S Dalla E Dragani TA Fletcher CF Forrest A Frazer KS Gaasterland T Gariboldi M Gissi C Godzik A Gough J Grimmond S Gustincich S Hirokawa N Jackson IJ Jarvis ED Kanai A 《Nature》2002,420(6915):563-573
159.
160.