The severe combined immune deficiency (SCID) mouse was reported as an animal model for human immune deficiency. Through the course of several studies, the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) gene came to be considered a candidate for the SCIDresponsible gene. We isolated an ORF of the murine DNAPKcs gene from SCID mice and their parent strain C.B-17 mice and determined the DNA sequences. The ORF of the murine DNA-PKcs gene contained 4128-aa residues and had 78.9% homology with the human DNA-PKcs gene. A particularly important finding is that a T to A transversion results in the substitution of termination codon in SCID mice for the Tyr-4046 in C.B-17 mice. No other mutation was detected in the ORF of the gene. The generality of this transversion was confirmed using four individual SCID and wild-type mice. The substitution took place in the phosphatidylinositol 3-kinase domain, and the mutated gene encodes the truncated products missing 83 residues of wild-type DNA-PKcs products. Furthermore, the quantity of DNA-PKcs transcript in wild-type and SCID cells was almost equal. These observations indicate that the DNA-PKcs gene is the SCID-responsible gene itself and that the detected mutation leads to the SCID aberration.

No abstract

No abstract

The excitation spectrum of the 2.8-eV luminescence band of crystalline Si02 has been measured in a photon energy range between 6 and 14 eV at 77 K. We find that the onset of the 2.8-eV luminescence occurs at 8.3 eV, which is nearly equal to the fundamental optical absorption edge of SiOz. This result supports strongly the model that the band is due to the radiative recombination of the self-trapped excitons.Irradiation of Si02 with ionizing radiation at low temperatures gives rise to strong blue luminescence, ' the origin of which has been a topic of interest. The blue luminescence, which is known to be a composite, has been suggested to include the radiative recombination of the self-trapped excitons. So far only the excitation spectra for the composite have been obtained, and the spectrum for the luminescence due to the self-trapped excitonsis not yet known.The composite nature of the blue luminescence was first demonstrated by the change in the luminescence spectrum with temperature.Two distinct bands at 2.5 and 2.8 eV have been identified by measurements of the polarization characteristics of the x-ray-induced luminescence in crystalline Si02 by Tanimura and Halliburton.They showed that the 2.5-eV band is polarized perpendicular to the z axis (threefold axis of the crystal) and that the 2.8-eV band is parallel to the z axis. We showed that the 2.5-eV band has a decay time of 1.2 ms at 80 K, while the 2.8-eV band has a decay time of 940 ps at the same temperature.Other workers have obtained several peaks for the blue luminescence by comparing the luminescence spectra at several temperatures.For instance, Alonso etal. have found peaks at 2.8, 2.9, and 3.2 eV. Since their spectrometer was not calibrated, the peak energies are not accurate and their 2.8 and 2.9-eV bands have been ascribed to the 2.5 and 2.8-eV band, respectively.Trukhin and Plaudis and Trukhin have observed a peak at 2.6 eV but their peak appears to be a composite of 2.5 and 2.8 eV bands, in view of their studies of the temperature dependence. Kristianpoller has observed the peaks at 2.8, 3.26, and 3.54 eV. Grinfelds, Aboltyn, and Plekhanov have observed a broad peak at 2.5 eV, and showed also that introduction of Cu impurities produces a band at 3.4 eV. Summarizing these observations, all of the authors have observed a luminescence band around 2.8 eV, but the presence of other peaks depends on the specimen. Furthermore, the results that the intensity of the 2.5-eV band saturates with increasing the intensity of the excitation appears to indicate that the band arises from defects or impurities. Thus it is most likely that only the 2.8-eV band is intrinsic.Further detailed information has been accumulated on the 2.8-eV luminescence band. It has been shown' that its intensity is proportional to the density of excitation up to about 10' cm . Time-resolved optical absorption measurements have indicated the presence of two allowed optical transitions at 5.2 and 4.2 eV from the initial state of the luminescence to higher states. A transient volume chan...

No abstract

No abstract

No abstract

No abstract