Preliminary crystallographic data for Azotobacter cytochrome c5.
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Biomedical subjects
Publications and source records attributed to C D Stout.
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The (omega', omega) polot depicting the internucleotide P-O bond rotation angles in yeast phenylalanyl transfer RNA has established the interdependence of the phosphodiesters and the nucleotide geometries in the folding of the polynucleotide backbone. The plot distinguishes the regions characteristic of secondary helical structures and tertiary structural loops and bends. The folding of the polynucleotide chain is accomplished either solely by rotations around the P-O bonds or in concert with rotations around the nucleotide C4'-C5' bond with or without changes in the sugar ring pucker. In spite of differences in nucleotide sequence and intraloop tertiary interactions in the anticodon and pseudouridine loops, a characteristic repeating structural unit is found for the sugar-phosphate backbone of the tetranucleotide segment around the sharp turns.
The atomic coordinates of yeast tRNA(Phe) in the monoclinic crystal form have been determined by an independent analysis from a model built into a 3 A MIR map. The overall molecular structure is found to be in agreement with those reported for the same crystal form by Ladner et al. (1975) and for the orthorhombic form by Quigley et al. (1975) and Kim et al. (1975). However, significant differences between any two of the four models are found in certain local regions of the molecule. The structure is analyzed in terms of the nucleotide stereochemistry and internucleotide phosphodiesters. A striking observation is that the majority of the nucleotide moieties occur in the conformation preferred by the constituent mononucleotides themselves. The internucleotide P-O bonds afford the primary source of flexibility for the folding of the polynucleotide backbone while the sugar pucker and C(4')-C(5') torsions provide the secondary source of flexibility.