Imagerie PI2

@article{,

title = {X-ray-induced debromination of nucleic acids at the Br K absorption edge and implications for MAD phasing},

author = {E Ennifar and P Carpentier and J L Ferrer and P Walter and P Dumas},

url = {http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12136136},

isbn = {12136136},

year  = {2002},

date = {2002-01-01},

journal = {Acta Crystallogr D Biol Crystallogr},

volume = {58},

number = {Pt 8},

pages = {1262-1268},

abstract = {Multi-wavelength anomalous dispersion (MAD) using brominated derivatives is considered a common and convenient technique for solving chemically synthesized nucleic acid structures. Here, it is shown that a relatively moderate X-ray dose (of the order of 5 x 10(15) photons mm(-2)) can induce sufficient debromination to prevent structure determination. The decrease in bromine occupancy with radiation dose can be accounted for by a simple exponential, with an estimated rate constant at the absorption-peak wavelength, 7.4 (0.8) MGy, that is not significantly different from its value at the absorption-edge wavelength, 9.2 (2.6) MGy (the given e.s.d.s assess the relative closeness of the two values, not their absolute accuracy, which is probably worse). Chemically, these results (and others) are consistent with bromine cleavage resulting from direct photodissociation and/or from the action of free electrons, rather than from the action of hydroxyl radicals originating from water dissociation. The free bromine species (Br(-)) diffuse too quickly, even in amorphous ice around 100 K, to allow the determination of a diffusion coefficient. From a practical point of view, it is suggested that a single data collection with a crystal consisting of iodinated instead of brominated derivatives could provide both anomalous scattering and SIR phase information by the progressive cleavage of iodine.},

note = {0907-4449 

Journal Article},

keywords = {Bromine/chemistry/radiation effects  Crystallography, ENNIFAR, Non-U.S. Gov't  X-Rays, Unité ARN, Viral/chemistry  Support, X-Ray  HIV-1/chemistry  Molecular Structure  Nucleic Acids/*chemistry/radiation effects  RNA},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Involvement of a GNRA tetraloop in long-range RNA tertiary interactions},

author = {L Jaeger and F Michel and E Westhof},

url = {http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=7510342},

isbn = {7510342},

year  = {1994},

date = {1994-01-01},

journal = {J Mol Biol},

volume = {236},

number = {5},

pages = {1271-1276},

abstract = {Terminal loops with a GNRA consensus sequence are widespread in RNA. It has been suggested that these loops act as "anchors" during tertiary folding, by interacting in a sequence-specific way with helices at distant locations along the molecule. We now show that a GUGA loop changes state upon disruption of the tertiary architecture of a self-splicing group I intron. Successful replacement of the postulated loop-helix contact by classical base-pairing points to binding of the loop into the shallow (minor) groove of the helix, as also indicated by partial restoration of ribozyme stability upon a specific double nucleotide substitution.},

note = {0022-2836 

Journal Article},

keywords = {Bacteriophage T4  Base Sequence  Hydrogen Bonding  Introns  Molecular Sequence Data  *Nucleic Acid Conformation  RNA/*chemistry  RNA, Non-U.S. Gov't, Unité ARN, Viral/chemistry  Support},

pubstate = {published},

tppubtype = {article}

}