title: Location of aromatic amino acids and belix content in Escherichia coli ribonucleic acid polymerase.
abstract: 1. The perturbing effect of glycerol on the direct spectrum of Escherichia coli DNA-dependent RNA polymerase has been studied. 2. By comparison with model compounds and with the unfolded polymerase in 3.8m-urea it was possible to determine the ratio of tyrosine and tryptophan residues present. On reduction of the urea-treated enzyme with 2-mercaptoethanol, no further change in the difference spectrum occurred. 3. The amino acid composition of the enzyme is given. 4. In the intact protein approx. 30% of the tryptophan and 54% of the tyrosine residues were exposed. In conjunction with the extinction value and molecular weight this corresponded to 7 tryptophan residues and 57 tyrosine residues on the surface and 16 tryptophan residues and 48 tyrosine residues ;buried'. 5. The optical rotatory dispersion of the enzyme was unaffected by 20% glycerol. 6. The helix content calculated from Moffit plots over 560-300nm was 13%, and from the 233nm trough 13%.
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D004926:Escherichia coli / Q000201:enzymology*; D005990:Glycerol; D008623:Mercaptoethanol; D008967:Molecular Biology; D009905:Optical Rotatory Dispersion; D012316:RNA Nucleotidyltransferases / Q000032:analysis*; D013057:Spectrum Analysis; D014364:Tryptophan / Q000032:analysis; D014443:Tyrosine / Q000032:analysis; D014508:Urea
chemical_list: D000596:Amino Acids; D014443:Tyrosine; D008623:Mercaptoethanol; D014364:Tryptophan; D014508:Urea; D012316:RNA Nucleotidyltransferases; D005990:Glycerol