Neuronal PAS domain protein 2 (NPAS2) is a circadian rhythm-associated transcription factor with two heme-binding sites on two PAS domains. In the present study, we compared the optical absorption spectra, resonance Raman spectra, heme-binding kinetics and DNA-binding characteristics of the isolated fragment containing the N-terminal basic helix-loop-helix (bHLH) of the first PAS (PAS-A) domain of NPAS2 with those of the PAS-A domain alone. We found that the heme-bound bHLH-PAS-A domain mainly exists as a dimer in solution. The Soret absorption peak of the Fe(III) complex for bHLH-PAS-A (421 nm) was located at a wavelength 9 nm higher than for isolated PAS-A (412 nm). The axial ligand trans to CO in bHLH-PAS-A appears to be His, based on the resonance Raman spectra. In addition, the rate constant for heme association with apo-bHLH-PAS (3.3 x 10(7) mol(-1) x s(-1)) was more than two orders of magnitude higher than for association with apo-PAS-A (< 10(5) mol(-1) x s(-1)). These results suggest that the bHLH domain assists in stable heme binding to NPAS2. Both optical and resonance Raman spectra indicated that the Fe(II)-NO heme complex is five-coordinated. Using the quartz-crystal microbalance method, we found that the bHLH-PAS-A domain binds specifically to the E-box DNA sequence in the presence, but not in the absence, of heme. On the basis of these results, we discuss the mode of heme binding by bHLH-PAS-A and its potential role in regulating DNA binding.

To explain and engineer intrinsic point defect behavior in large-diameter single crystal Si grown using the Czochralski (CZ) method, a unified model valid for all pulling processes, crystal resistivities, and electrically inactive impurity concentrations that couples the effects of thermal stress, dopants, and interstitial oxygen (O i ) atoms is needed. We determined the thermal equilibrium concentration of intrinsic point defects (vacancy V and self-interstitial Si I) in CZ-Si crystal as functions of thermal stresses, type and concentration of dopant, and the concentration of O i atoms. Global heat transfer during crystal growth in a puller was simulated using STR Group's CGSim software package. A visual distribution of V and I concentrations inside a growing doped and thermally stressed Si ingot is very useful for improving the quality of large-diameter CZ-Si crystals.

Anisotropic thermal stress near the melt/solid interface during growth of a Si crystal from a melt significantly affects control of grown-in defects when the diameter of the growing crystal is large. This effect on the behavior of intrinsic point defects in a growing Si crystal with 300-mm diameter was investigated by calculations and experiments. One has to take into account this effect in the development of a crystal-pulling process for 450-mm-diameter defect-free Si crystals.

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