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51.
Lactose is shown to be an effective anti-inducer of the lac operon both in vivo and in vitro. When lactose is used as a carbon source, the synthesis of β-galaetosidase in Escheriahia coli is not fully induced. Moreover, lactose is able to partially inhibit induction by isopropyl-(β-d-thiogalactoside in strains synthesizing inactive as well as active β-galactosidase. These effects in vivo are not due to catabolite repression by the glucose derived from lactose. These in vivo results suggest that lactose is acting as an anti-inducer. This is confirmed in vitro by showing that lactose binds to the lac represser and stabilizes the represser-operator complex. 相似文献
52.
Dominique Bourgeois 《Structure (London, England : 1993)》2009,17(11):1427-1428
53.
lac Repressor-operator interaction. IX. The binding of lac repressor to operators containing Oc mutations 总被引:18,自引:0,他引:18
Representative members of the six classes of operator constitutive (Oc) point mutations, which have been mapped and well characterized in vivo, were crossed into λφ80 lac phages. The phage DNAs containing the Oc mutations were used to measure the affinity of the lac repressor (R) for each Oc operator by determining the half-lives of the different ROc complexes in vitro. The results provide evidence that: (a) the higher the constitutive level of β-galactosidase in vivo, as the result of an Oc mutation, the lower the affinity of the lac repressor for that Oc operator, with a maximum difference of two orders of magnitude in affinity of the repressor for the highest Oc tested as compared to the wild type O+ operator; (b) the six classes of Oc operators appear to be twofold degenerate, in that two members of each class, which were previously distinguished by mapping, have the same affinity for the lac repressor; (c) an inducer and an anti-inducer have the same effect on the ROc complexes as on the RO+ complexes; (d) the relationship between induction ratios in vivo and the binding constant of the repressor for each Oc mutation in vitro does not follow the mass action equation but rather a more complex dependency, which is discussed.These results suggest a functional symmetry in the lac operator. 相似文献
54.
Cyclic AMP-dependent protein kinase modulation of the glucocorticoid-induced cytolytic response in murine T-lymphoma cells 总被引:3,自引:0,他引:3
The antiproliferative effect of glucocorticoid hormones on lymphoid tissue serves as the basis for their use in chemotherapy of lymphomas and leukemias. The effectiveness of the steroid-mediated response is potentially contingent upon a variety of factors, including the cellular level of glucocorticoid receptors. This report demonstrates that differences in the expression of the glucocorticoid receptor gene can modulate steroid sensitivity of individuals within a population of lymphoma cells. We have also found that loss of cAMP-dependent protein kinase activity caused a measurable decrease of steroid sensitivity in the murine T-lymphoma WEHI-7 without producing a significant change in steroid binding capacity. However, the extent of this change in sensitivity was dependent upon the level of glucocorticoid receptor expression. Lymphoma cells containing few spare steroid receptors became significantly resistant to glucocorticoids through loss of cAMP-dependent kinase function. On the other hand, elevated levels of cAMP were found to cause an increase in glucocorticoid receptor mRNA concentrations. Thus, cAMP-dependent protein kinase activity has the potential to modulate a lymphoma cell's steroid sensitivity by affecting the level of glucocorticoid receptor expression as well as the receptor's efficiency in producing a cytolytic response. 相似文献
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59.
Estelle Villemont Frédéric Dubois Rajbir S. Sangwan Gérard Vasseur Yvan Bourgeois Brigitte S. Sangwan-Norreel 《Planta》1997,201(2):160-172
Chimeric -glucuronidase (GUS) gene expression in an efficientAgrobacterium-mediated transformation system utilising mesophyll cells ofPetunia hybrida synchronized with cell cycle phase-specific inhibitors (mimosine and colchicine) was used to show the absolute requirement of S-phase for transfer and/or integration of the transferred DNA (T-DNA). Flow-cytometric analysis of nuclear DNA content and immunohistological detection of bromodeoxyuridine (BrdUrd) incorporation showed that, prior to phytohormone treatment, most (98%) mesophyll cells were at GO-Gl-phase (quiescent phase) and no cell division was occurring. After 48 h and 72 h of phytohormone treatment, there was a rapid increase in S-G2-M-phase populations (> 75%) and a concomitant decrease (down to 24%) in G0–-G1-phase cells. Assays of GUS showed that maximum transformation (> 95% of explants) also occurred after this period. Our data showed that mimosine and colchicine blocked the mesophyll cells at late Gl-phase and M-phase, respectively. No transformation (= GUS expression) was observed in phytohormone-treated cells inhibited in late G1 by mimosine. However, after removal of mimosine, 82% of the explants were transformed, indicating the non-toxic and reversible effect of the inhibitor. On the other hand, a relatively high transformation frequency (65% of explants) was observed after blocking the cell cycle at M-phase with colchicine. However, only transient, but no stable, gene expression (= kanamycin-resistant callus formation) was observed in colchicine-treated M-phase-arrested cells. Similarly, endoreduplication of nuclear DNA, which occurred during the 48 h of phytohormone treatment in some mesophyll cells and cells located along the minor veins in the leaf explants, resulted in transient GUS expression only. These observations indicate a direct correlation between endoreduplication and transient GUS gene expression. Obviously, for stable GUS gene expression, cell division and proliferation are required, indicating that both DNA duplication (S-phase) and cell division (M-phase) are strongly related to stable transformation. We propose that the present system should facilitate further dissection of the process of T-DNA integration in the host genome and therefore should aid in developing new strategies for transformation of recalcitrant plants.Abbreviations BAP
6-benzylaminopurine
- BM
basal medium
- BrdUrd
bromodeoxyuridine
- GUS
-glucuronidase
- KmR
kanamycin resistant
- T-DNA
transferred DNA 相似文献
60.
Prophylactic Administration of a Complementarity-Determining Region Derived from a Neutralizing Monoclonal Antibody Is Effective against Respiratory Syncytial Virus Infection in BALB/c Mice
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Immunotherapy with antibodies against respiratory syncytial virus (RSV) is a treatment option given the absence of any vaccine or other available satisfactory treatment. We selected one of our monoclonal antibodies, RS-348, that is highly neutralizing. We showed that a single peptide (PEP3H) derived from complementarity-determining region 3 (CDR3) of its heavy chain was capable of neutralizing the virus in vitro. When intranasally administered 24 h before challenge, this peptide protected BALB/c mice against RSV lung infection. These results indicate that a single CDR can be effective against RSV infection. 相似文献