VNMR software

NOESY was performed at 32 °C on a VXR-500 spectrometer operating at a proton frequency of 500 MHz. The protein was dissolved in 20 mM sodium phosphate, pH 7.5 (direct pH meter reading), 100 mM NaCl, 5 mM DTT in D2O. The protein concentration was 2 mM. The data was acquired in the hypercomplex mode with a mixing time of 150 ms (Jeener et al., 1979 Macura Ernst,1980). The spectral width was 7200 Hz in both dimensions. 2048 complex points in the t2 dimension and 256 complex points in the tl dimension were acquired. 96 transients were collected for each FID. Data processing was performed on a Sun Sparc 10 station using VNMR software from Varian. The time domain data were zero-filled once and multiplied by shifted sinebell or Gaussian functions before Fourier transformation in both dimensions. Chemical shifts were referenced to internal sodium 3-(trimethylsilyl)-propionate-2,2,3,3-d4. 

Fig. 3. A comparison of a l5N-HSQC experiment (a) and a TROSY experiment (b) on the 30-kDa complex of the l5N,L1C-0 subunit and the unlabelled N-terminal domain (1-185) subunit of DNA polymerase III. The spectra were recorded on a Varian INOVA 600 spectrometer operating at a H frequency of 600MHz. Spectra were acquired with 96 (/,)x 1024 (r2) complex points and processed using VNMR software.

The WURST decoupling sequence was implemented with the Pbox in Varian s VNMR software, using a constant adiabaticity modulated frequency, a 0.92 ms pulsewidth, and a 1.2 adiabaticity frictor (Q). The constant radiofiequency level yBaCrms) was 4.3 kHz. In order to compensate for residual imperfections in spin inversion, the five-step phase cycle (0 , 60°, 150°, 60°, 0°) of Tycko et al (3) was used. 

MD3M was obtained from Dow Coming Corporation. 200 mg of this colorless oil was dissolved in 0.7 ml CDCU solvent and put into a 5-mm NMR tube for the following NMR measurements. All NMR spectra were collected at 25 °C on a Varian Unityp/w 750 MHz NMR spectrometer equipped with four RF channels, a Performa II z axial pulse field gradient (PFG) accessory, a 5 mm Varian H/ C/X (where X is tunable over the range of the resotumce frequencies firom N to Cd) triple resonance four charmel probe with a PFG coU (for ID H, 2D and 3D NMR experiments), and a 5 mm Varian H/ X (X = P- N) switchable probe with a PFG coil (for ID C and Si NMR experiments). The solvent was also used as the internal reference for H and C chemical shifts. TMS was used as an external reference for Si chemical shifts. All data were processed with Varian s VNMR software on a SUN Ultra-10 workstation. 

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