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排序方式: 共有361条查询结果,搜索用时 31 毫秒
1.
2.
Translational repression: biological activity of plasmid-encoded bacteriophage T4 RegA protein 总被引:9,自引:0,他引:9
E S Miller J Karam M Dawson M Trojanowska P Gauss L Gold 《Journal of molecular biology》1987,194(3):397-410
The RegA protein of bacteriophage T4 is a translational repressor that regulates expression of several phage early mRNAs. We have cloned wild-type and mutant alleles of the T4 regA gene under control of the heat-inducible, plasmid-borne leftward promoter (PL) of phage lambda. Expression of the cloned regA+ gene resulted in the synthesis of a protein that closely resembled phage-encoded RegA protein in biological properties. It repressed its own synthesis (autogenous translational control) as well as the synthesis of specific T4-encoded proteins that are known from other studies to be under RegA-mediated translational control. Cloned mutant alleles of regA exhibited derepressed synthesis of the mutant regA gene products and were ineffective in trans against RegA-sensitive mRNA targets. The effects of plasmid-encoded RegA proteins were also demonstrated in experiments using two compatible plasmids in uninfected Escherichia coli. The two-plasmid assays confirm the sensitivities of several cloned T4 genes to RegA-mediated translational repression and are well-suited for genetic analysis of RegA target sites. Repression specificity in this system was demonstrated by using wild-type and operator-constitutive translational initiation sites of T4 rIIB fused to lacZ. The results show that no additional T4 products are required for RegA-mediated translational repression. Additional evidence is provided for the proposal that uridine-rich mRNA sequences are preferred targets for the repressor. Surprisingly, plasmid-generated RegA protein represses the synthesis of some E. coli proteins and appears to enhance selectively the synthesis of others. The RegA protein may have multiple functions, and its binding sites are not restricted to phage mRNAs. 相似文献
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5.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
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Inhibition of the rat adrenal ornithine decarboxylase activity by immobilization stress and/or dexamethasone 总被引:2,自引:0,他引:2
Karam F.A. Soliman R.Renee Reams Matty O. Udoye Vani K. Nonavinakere 《Life sciences》1997,60(26):E1010-2387
The effects of immobilization stress and/or dexamethasone (DEX) on the adrenal ornithine decarboxylase (ODC) activities of sham-operated and adrenal-medulloectomized (enucleated) male Sprague-Dawley rats were investigated. On day 11 after surgery, rats were injected with saline or DEX (1 mg/kg), 3 h before the time of sacrifice (0600 h or 1800 h). Four groups, from sham-operated and enucleated rats (ENU) treated with saline or DEX were subjected to immobilization stress for 1 h prior to sacrifice. Groups of rats from stress-sham-DEX, non stress-sham-DEX, stress-sham, non stress-sham, stress-ENU-DEX, non stress-ENU-DEX, stress-ENU, and non stress-ENU were sacrificed at 0600 h or 1800 h on day 11 after surgery. Adrenal glands were excised and later analyzed for ODC activities. Results indicated that DEX and/or immobilization stress inhibited ODC activities (p < 0.05) in normal and regenerating adrenal glands at 1800 h and ODC activity varies diurnally, the activity being greater at 1800 h than at 0600 hours (p < 0.001). 相似文献
8.
Lynne H. Claye Hyacinth C. Akunne M. Duff Davis Steve DeMattos Karam F. A. Soliman 《Molecular neurobiology》1995,11(1-3):55-66
In order to determine whether repeated cocaine administration produced persistent changes in dopamine (DA) receptor binding and release consistent with behavioral sensitization, rats were treated with either cocaine (25 mg/kg ip) or saline twice daily for 14 consecutive days followed by a 3-d withdrawal period. The DA transporter site was assayed using [3H]GBR 12935, whereas D1 and D2 sites were assayed using [3H]SCH 23390 and [3H]spiperone, respectively. The density (B max) of the DA transporter binding sites in the ST of the cocaine-treated group increased significantly (p<0.05) over controls 3 d after the last injection, whereas the density of striatal D1 and D2 binding sites remained unchanged. The DA transporter in the nucleus accumbens (NA) was also studied with [3H]GBR 12935 and was unchanged following drug treatment. D1 and D2 binding parameters for the NA were not determined in this study. Furthermore, cocaine administration did not affect the affinities (K d ) of the radioligands used to label the transporter, D1, or D2 sites in any of the studies performed. In addition, striatal DA release was measured using in vivo microdialysis in anesthetized rats. Linear regression analysis on maximal decreases in DA release after apomorphine (0.02, 0.2, and 2.0 mg/kg sc) injection showed no difference in the functional capacity of the ST to modulate DA transmission between control and treated groups. Moreover, animals pretreated with cocaine showed a significant (p<0.01) decrease in locomotor activity (LA) after a presynaptic, autoregulating dose of apomorphine (0.03 mg/kg sc) was given. These results suggest that the effects seen after repeated exposure to cocaine may be regulated, in part, by changes in striatal DA transporter binding site densities and not necessarily by DA-releasing mechanisms or D1 and D2 receptor modification. 相似文献
9.
M S Nolte C Taboga E Salamon A Moses J Longenecker J Flier J H Karam 《Hormones et métabolisme》1990,22(3):170-174
Nasally administered (IN) insulin has been advocated as a potentially useful alternative to subcutaneously administered regular insulin because of its more rapid onset and time to peak action and its shorter duration of action. This study further defines the pharmacodynamics of IN insulin by using a euglycemic clamp technique to determine the bioavailability of IN insulin as compared with intravenous (IV) insulin, and to ascertain whether multiple sequentially administered doses of IN insulin alter pharmacodynamics. Eight normal volunteers received 2 control doses of IV insulin (0.05 U/kg), and 3 high doses (0.7 U/kg) and 3 low doses (0.35 U/kg) of IN insulin with an absorption enhancer (tauro-24,25 dihydrofusidate) given sequentially over a 2 day period. A euglycemic clamp was performed with a Biostator (Ames) that infused dextrose to keep the subject's blood glucose at his fasting level. Analysis of dextrose infusion curves for the low and high doses of IN insulin revealed an onset of action of 9.4 +/- 0.4 and 10.5 +/- 0.3 minutes, time to peak action of 20.6 +/- 5.6 and 23.7 +/- 4.4 minutes and duration of action of 82.1 +/- 5.2 and 95 +/- 5.7 minutes respectively. Both the onset of action and time to peak action were slightly longer (P less than .05) for the high as compared with the low dose IN insulin, although this should not represent a clinically significant difference. The total dextrose requirement was 21.9 +/- 2.3 g for the low dose IN insulin and 34.1 +/- 3.3 g for the high dose IN insulin, the latter value being significantly greater (P less than .01) than the former.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
10.
Karam El-Bayoumy Edmond J. Lavoie Stephen S. Hecht Elizabeth Ann Fow Dietrich Hoffmann 《Mutation research》1981,90(2):143-147
Mitogen-stimulated lymphocytes from 8 healthy donors were exposed to interferon, and cytogenetic studies were preformed. The response of lymphocytes to the mitogens phytohemagglutinin (PHA), concanavalin A (con A) and pokeweed mitogen (PWM) was inhibited by interferon, whereas an increased number of structural chromosomal aberrations was not detected. Further investigations of the cytogenetic effects of interferon are needed. 相似文献