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排序方式: 共有393条查询结果,搜索用时 15 毫秒
1.
B Crabtree 《FEBS letters》1985,187(2):193-195
A system of enzymically interconvertible enzyme forms (interconversion cycle) is known to increase the sensitivity to regulators. Here it is shown that this system may also provide a discrete switching mechanism in which the response is maintained when the stimulus is removed. These switches may be important in producing discontinuous metabolic changes such as those associated with cell differentiation. 相似文献
2.
3.
1. Equations for control coefficients are derived by using a method that generates all the control coefficients for a system in a single procedure. This requires solving fewer simultaneous equations than an equivalent method based on 'control theorems'. 2. The interpretation of control coefficients is discussed: in particular, it is shown that these functions are unsatisfactory as measures of 'control' and are perhaps best used as a means of testing control theories (models). 相似文献
4.
Characterization of antigen receptor response elements within the interleukin-2 enhancer. 总被引:51,自引:12,他引:39
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D B Durand J P Shaw M R Bush R E Replogle R Belagaje G R Crabtree 《Molecular and cellular biology》1988,8(4):1715-1724
T-cell activation and induction of interleukin-2 (IL-2) expression in human T lymphocytes require both interaction of foreign antigen with the T-cell antigen receptor and protein kinase C (PKC) stimulation. Agents such as phorbol 12-myristate 13-acetate (PMA) that stimulate PKC augment the effects of antigen but are not sufficient for IL-2 activation. By analysis of deletion mutants, we identified three DNA sequences extending from -73 to -89, -217 to -255, and -263 to -279, designated IL-2 sites A, D, and E, respectively, that are required for maximal induction of IL-2 expression. One of these regions, site E, interacted with a protein (NF-IL-2E) present only in the nuclei of cells which have been stimulated. The other two sequences interacted with a protein (NF-IL-2A) that is constitutively expressed in T cells. When multiple tandem copies of either the E site or the A site were placed upstream of the gamma-fibrinogen promoter, they activated expression via this promoter in response to signals initiated at the antigen receptor but not following PMA stimulation. For this reason, we denoted them antigen receptor response elements. The uncoupling of antigen receptor and PKC requirements in these studies indicates that these signal pathways are, at least in part, distinct and integrated at the level of the gene. 相似文献
5.
Roy E. Crabtree Edward C. Cyr Renée E. Bishop Laura M Falkenstein John M. Dean 《Environmental Biology of Fishes》1992,35(4):361-370
Synopsis Leptocephali were collected in June 1981 and July 1989 over the continental shelf and slope of the Florida west coast. Tarpon larvae ranged 5.5–24.4 mm standard length (SL) and were the second most abundant leptocephalus species. Sagittae examined with compound microscopes and scanning electron microscopy had increments that were presumed to be formed daily. Increment counts made using the two microscopic techniques were not significantly different. Estimated ages ranged 2–25 days with a growth rate (± standard error) of 0.92 ± 0.04 mm d–1 The least squares linear regression equation SL = 2.78 + 0.92 (age in days) best described the relationship between estimated age and length. Adult tarpon appear to undergo a substantial spawning migration from inshore areas frequented during spring and summer to offshore spawning grounds. Spawning occurs during May, June, and July, although the spawning season may be of greater duration. 相似文献
6.
A J Fornace D E Cummings C M Comeau J A Kant G R Crabtree 《The Journal of biological chemistry》1984,259(20):12826-12830
The gamma chain of human fibrinogen exists in 2 nonallelic forms, gamma A and gamma B, which differ only in their carboxyl termini. We have found that only one genomic locus exists for gamma-fibrinogen and that the gamma A and gamma B chains arise by alternate mRNA splicing near the 3' end of this gene. In contrast to the rat gamma B mRNA which is produced by alternate splicing with identical polyadenylation sites, human gamma B is produced when the eighth intervening sequence remains unspliced and a polyadenylation signal within this intron is used. The new carboxyl terminus is 16 amino acids longer than the gamma A protein, and although there is only minimal homology between the rat and human carboxyl termini they share a very high proportion of acidic amino acids. 相似文献
7.
B Y Karlan J A Rivero M E Crabtree B A Littlefield 《Molecular endocrinology (Baltimore, Md.)》1989,3(6):1006-1013
Previous studies from our laboratory have demonstrated that OVCA 433 human ovarian carcinoma cells are glucocorticoid responsive by several criteria and contain high affinity, saturable, steroid-specific glucocorticoid receptors. These cells secrete both mammalian plasminogen activators (PAs), urokinase (uPA) and tissue-type PA (tPA). Treatment of OVCA 433 cells with 1 x 10(-7) M dexamethasone (Dex) for 4 days led to 77% and 83% reductions in the extracellular activities of uPA and tPA, respectively, released into serum-free conditioned medium during a 1-h period. Dex treatment led to a 71% decrease in the rate of extracellular uPA antigen accumulation, as determined by enzyme-linked immunosorbent assay, as well as a 73% reduction in steady state uPA mRNA levels. In contrast, Dex treatment led to only a 42% decrease in the rate of extracellular tPA antigen accumulation and a 48% decrease in tPA mRNA levels; such decreases were insufficient to account for the 83% reduction in tPA activity. Thus, while Dex-induced decreases in uPA antigen and mRNA levels accounted for all but 6% of the decrease in uPA activity, a large discrepancy existed between the magnitudes of decreased tPA activity and decreased tPA antigen and mRNA levels. OVCA 433 cells produce both PAI-1 and PAI-2, two specific PA inhibitors. Treatment of cells with 1 x 10(-7) M Dex for 4 days led to a 3.3-fold increase in the rate of extracellular PAI-1 accumulation, with little or no effect on PAI-2 accumulation.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
8.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
9.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
10.
The intracellular location of pyruvate carboxylase, citrate synthase and 3-hydroxyacyl-CoA dehydrogenase in lactating rat mammary gland. 总被引:1,自引:1,他引:0
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The intracellular location of pyruvate carboxylase (EC 6.4.1.1), citrate synthase (EC 4.1.3.7) and 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) in rat mammary gland was investigated by using a fractional-extraction technique. The results indicate a mitochondrial location for all three enzymes. 相似文献