The POU transcription factor Oct-4 is a master regulator affecting the fate of pluripotent embryonic stem cells. However, the precise mechanisms by which the activation and expression of Oct-4 are regulated still remain to be elucidated. We describe here a novel murine ubiquitin ligase, Wwp2, that specifically interacts with Oct-4 and promotes its ubiquitination both in vivo and in vitro.

Single-walled carbon nanotubes (SWCNTs) have been extensively studied since they were discovered by Iijima in 1991, [1] and in particular many SWCNT-based electrical devices have been fabricated and evaluated. [2,3] These devices include field-effect transistors (FETs) [4][5][6][7][8] and diodes. [9][10][11][12][13][14] When contacted with Pd and Sc, [7,15] it has been shown that carriers can be injected, barrier-free, into the valence band (p-FET) [7] and conduction band (n-FET), [15] respectively, forming the basis for doping-free carbon nanotube (CNT)-based ballistic complementary metal-oxide semiconductor (CMOS) technology.[15] Similar to Si-based CMOS, [16] the CNT-based CMOS inverter (Fig. 1a) forms the simplest and most fundamental unit for more complex CMOS circuits. In this Communication we show, in addition to the usual CMOS inverter functions, that this basic device unit can also be readily configured to function as an effective ambipolar FET [17] and a new type of diode: the barrier-free bipolar diode. Several CNT-based diodes have been developed. These include p-n junction diodes formed by chemical doping [9] and split gates, [10] and Schottky diodes based on intramolecular junctions [11] and metal-CNT junctions. [12][13][14] While the functioning of the p-n junction diode relies on the diffusion of minority carriers in the device, which limits its high-speed applications, [14] the presence of the Schottky barrier (SB) in the Schottky diode significantly reduces the maximum current that may be achieved. In general, the conventional diode may be regarded as unipolar involving only one type of carrier, that is, either electrons or holes.In an earlier report, [15] we demonstrated that a CMOS inverter can be fabricated readily by depositing two Pd electrodes and two Sc electrodes side-by-side on a single CNT lying on the surface of a SiO 2 gate oxide. As shown in Figure 1a, when the two Pd electrodes are used as the source (S) and drain (D), the field effect of the device is characteristic of a p-type FET (see Supporting Information Fig. S1a). When the Sc electrodes are used, the device is characteristic of an n-type FET (see Fig. S1b). When all four electrodes are used, with V OUT ¼ V 2 ¼ V 3 and V IN ¼ V 5 , the device functions as a CMOS inverter (see Fig. S1c).It should be noted that in the Si-based CMOS inverter the conduction channel of the n-FET is isolated from that of the p-FET.[16] In the CNT-based inverter shown in Figure 1a, both p-and n-FETs share the same conduction channel, that is, the CNT. The n-FET can be isolated from the p-FET readily by cutting or etching away the CNT segment between the V 2 and V 3 electrodes, but Figure S1 demonstrates clearly that even though we did not disconnect the n-FET and p-FET we still obtained a high-performing CMOS inverter with a voltage gain of more than 10 and room temperature I on /I off ratios of more than 10 5 for both the p-and n-FETs. More than 30 devices were fabricated on the same CNT, and all of the devices showed almost the same I-V characteri...

Photovoltaic effects are studied for asymmetrically contacted single-walled carbon nanotube (SWCNT) barrierfree bipolar diode (BFBD) under infrared laser illumination. The BFBD is based on a SWCNT with a diameter d ∼ 1.5 nm and length L ∼ 800 nm, and the device shows a good open-circuit voltage of V OC ) 0.23V and large photocurrent I SC of more than 15 nA.

A significant visible light response of unintentionally doped ZnO nanowire (NW) field effect transistors (FETs) has been observed in a reversible manner (for illumination source on and off). In particular, under white light illumination (wavelength longer than 400 nm), the threshold voltage (V T) of the ZnO NW FET shifts greatly to the negative direction, suggesting a remarkable increase in carrier concentration. A photon-assisted oxygen molecule desorption mechanism is proposed to explain the observed sub-bandgap photoresponse on the basis of the behavior of the experimental devices in different gas atmospheres (air, vacuum, pure N2, and pure O2) and with/without nanowire surface modifications (coated with PMMA).