A H-1-NMR STUDY OF THE TRANSCRIPTION FACTOR-I FROM BACILLUS-SUBTILIS PHAGE SPO1 BY SELECTIVE H-2-LABELING - COMPLETE ASSIGNMENT AND STRUCTURAL-ANALYSIS OF THE AROMATIC RESONANCES FOR A 22-KDA HOMODIMER

H-1-NMR experiments have been performed on transcription factor 1 (TF1 ) encoded by Bacillus subtilis phage SPO1. To study this 22-kDa homodi meric DNA-binding protein, a selective H-2-labeling strategy has been employed. Complete sequence-specific assignments of all the resonances from the five aromatic residues were determined by a modified standar d sequential-assignment procedure. The reduced contribution of spin di ffusion upon the long-mixing-time nuclear-Overhauser-enhancement spect roscopy for the selectively H-2-labeled variants, as opposed to the fu lly H-1-containing protein, has allowed for the identification of the spin systems and of the long-range dipolar contacts between Phe28 and Phe47 protons in the protein core and between Phe61 and Phe97 protons. The latter suggests an interaction between the proposed beta-ribbon D NA-binding arm and the carboxy terminus of the paired monomer. A previ ously proposed TF1 structural model [Geiduschek, E. P, Schneider, G. J . & Sayre, M. H. (1990) J. Struct. Biol. 104, 84-90)] has been modifie d using constrained-energy-minimization calculations incorporating the experimentally determined set of aromatic-to-aromatic contacts. This new model has been analyzed with regard to the relative mobility and t he relative solvent accessibility of the aromatic residues which have been measured by the nonselective T1 relaxation times of the aromatic resonances for the fully H-1-containing protein and the relaxation tim e enhancements upon selective H-2-labeling, respectively.