Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phenomenon of superinduction refers to the process by which high concentrations of protein synthesis inhibitors augment and stabilize mRNA transcript levels, e.g. 36-180 microM of Puromycin (PM) has been found to elicit c-myc mRNA superinduction. The expression of the proto-oncogene c-myc has been strongly variously implicated in the regulation of the apoptotic cascade. Since we recently found that a low dose of the protein synthesis inhibitor PM activated the apoptotic cascade in HL-60 leukaemic cells, the current study was undertaken to examine c-myc mRNA transcript levels in such cells, and to assess the relationship, if any, between PM-elicited c-myc mRNA superinduction and subsequent activation of the apoptotic cascade. PM was employed in vitro at doses of 0.9 microM and 2 microM. Dose-dependent c-myc mRNA superinduction was present at 1 hour of PM-exposure, and was associated with subsequent activation of the apoptotic cascade at 24 hours of exposure. Apoptosis was confirmed morphologically as evidenced by chromatin condensation, nuclear fragmentation and the formation of apoptotic bodies, and by DNA agarose gel electrophoresis which showed the pattern of double-stranded DNA fragments that result from the activation of an endogenous endonuclease. [C14]Leucine incorporation studies at 1 hour demonstrated minimal protein synthesis inhibition at doses used, suggesting that c-myc mRNA superinduction in this context may have been the result of mechanisms which were independent of the inhibition of synthesis of new proteins, such as interruptions in signal transduction.
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PMID:Puromycin-elicited c-myc mRNA superinduction precedes apoptosis in HL-60 leukaemic cells. 829 42

The homing endonuclease I-PpoI severely bends its DNA target, resulting in significant deformations of the minor and major groove near the scissile phosphate groups. To study the role of conformational changes within the protein catalyst and the DNA substrate, we have determined the structure of the enzyme in the absence of bound DNA, performed gel retardation analyses of DNA binding and bending, and have mutagenized a leucine residue that contacts an adenine nucleotide at the site of cleavage. The structure of the L116A/DNA complex has been determined and the effects of the mutation on affinity and catalysis have been measured. The wild-type protein displays a rigid-body rotation of its individual subunits upon DNA binding. Homing site DNA is not detectably bent in the absence of protein, but is sharply bent in both the wild-type and L116A complexes. These results indicate that binding involves a large distortion of the DNA and a smaller change in protein conformation. Leucine 116 is critical for binding and catalysis: it appears to be important for forming a well-ordered protein-DNA complex at the cleavage site, for maximal deformation of the DNA, and for desolvation of the nucleotide bases that are partially unstacked in the enzyme complex.
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PMID:Conformational changes and cleavage by the homing endonuclease I-PpoI: a critical role for a leucine residue in the active site. 1089 Dec 75