Proper regulation of cell cycle progression is pivotal for maintaining genome stability. In a search for DNA damage-inducible, CHK1-modulated genes, we have identified BTG3 (B-cell translocation gene 3) as a direct p53 target. The p53 transcription factor binds to a consensus sequence located in intron 2 of the gene both in vitro and in vivo, and depletion of p53 by small interfering RNA (siRNA) abolishes DNA damage-induced expression of the gene. Furthermore, ablation of BTG3 by siRNA in cancer cells results in accelerated exit from the DNA damage-induced G2/M block. In vitro, BTG3 binds to and inhibits E2F1 through an N-terminal domain including the conserved box A. Deletion of the interaction domain in BTG3 abrogates not only its growth suppression activity, but also its repression on E2F1-mediated transactivation. We also present evidence that by disrupting the DNA binding activity of E2F1, BTG3 participates in the regulation of E2F1 target gene expression. Therefore, our studies have revealed a previously unidentified pathway through which the activity of E2F1 may be guarded by activated p53.

The cross-sectional sizes of the regularly patterned GaN nanorods (NRs) and InGaN/GaN quantum-well (QW) NRs of different heights and different hexagon orientations, which are grown on the patterned templates of different hole diameters, pitches, and crystal orientations, are compared. It is found that the cross-sectional size of the GaN NR, which is formed with the pulsed growth mode, is mainly controlled by the patterned hole diameter, and the thickness of the sidewall QW structure is mainly determined by the NR height. The cross-sectional size variation of GaN NR is interpreted by the quasi-three-dimensional nature of atom supply amount for precipitating a two-dimensional disk-shaped NR segment. The variation of the sidewall QW structure is explained by the condition of constituent atom supply in the gap volume between the neighboring NRs. Also, we compare the cathodoluminescence emission wavelengths among those samples of different growth conditions. Generally speaking, the QW NR with a smaller height, a larger cross-sectional size, or a larger pitch has a longer emission wavelength.

Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition Effect of buffer layers and stacking faults on the reduction of threading dislocation density in GaN overlayers grown by metalorganic chemical vapor deposition Threading dislocation ͑TD͒ evolution during patterned GaN nanocolumn ͑NC͒ growth and coalescence overgrowth with metal-organic chemical vapor deposition is studied based on the comparisons of NC and coalescence overgrowth samples of different NC cross-section diameters and spacing sizes. From the measurement results of depth-dependent x-ray diffraction and cross-section transmission electron microscopy, it is found that the TD density in an NC depends on the patterned hole size for NC growth. Also, the TD formation at the beginning of coalescence overgrowth is related to the NC spacing size. Although the TD density at the bottom of the overgrown layer is weakly dependent on NC and spacing sizes, at its top surface, the TD density strongly relies on NC size. Among the overgrowth samples of different NC diameters and spacing sizes with a fixed NC diameter/spacing ratio, the one with the smallest size and spacing leads to the lowest TD density, the largest lateral domain size, and the highest photoluminescence efficiency. Also, the optical and crystal qualities at the surfaces of all the overgrowth samples are superior to those of a GaN template.

With the nano-imprint lithography and the pulsed growth mode of metalorganic chemical vapor deposition, a regularly-patterned, c-axis nitride nanorod (NR) array of quite uniform geometry with simultaneous depositions of top-face, c-plane disc-like and sidewall, m-plane core-shell InGaN/GaN quantum well (QW) structures is formed. The differences of geometry and composition between these two groups of QW are studied with scanning electron microscopy, cathodoluminescence, and transmission electron microscopy (TEM). In particular, the strain state analysis results in TEM observations provide us with the information about the QW width and composition. It is found that the QW widths are narrower and the indium contents are higher in the sidewall m-plane QWs, when compared with the top-face c-plane QWs. Also, in the sidewall m-plane QWs, the QW width (indium content) decreases (increases) with the height on the sidewall. The observed results can be interpreted with the migration behaviors of the constituent atoms along the NR sidewall from the bottom.

To achieve green emission from the sidewall non-polar quantum wells (QWs) of a GaN nanorod (NR) light-emitting diode, regularly patterned InGaN/GaN QW NR arrays are grown under various growth conditions of indium supply rate, QW growth temperature, and QW growth time for comparing their emission wavelength variations of the top-face c-plane and sidewall m-plane QWs based on photoluminescence and cathodoluminescence (CL) measurements. Although the variation trends of QW emission wavelength by changing those growth conditions in the NR structure are similar to those in the planar structure, the emission wavelength range of the QWs on an NR is significantly shorter than that in a planar structure under the same growth conditions. Under the growth conditions for a longer NR QW emission wavelength, the difference of emission wavelength between the top-face and sidewall QWs is smaller. Also, the variation range of the emission wavelength from the sidewall QWs over different heights on the sidewall becomes larger. On the other hand, strain state analysis based on transmission electron microscopy is undertaken to calibrate the average QW widths and average indium contents in the two groups of QW of an NR. The variation trends of the calibrated QW widths and indium contents are consistent with those of the CL emission wavelengths from various portions of NR QWs.