A large-scale assay was performed by transfecting 29,910 individual cDNA clones derived from human placenta, fetus, and normal liver tissues into human hepatoma cells and 22,926 cDNA clones into mouse NIH 3T3 cells. Based on the results of colony formation in hepatoma cells and foci formation in NIH 3T3 cells, 3,806 cDNA species (8,237 clones) were found to possess the ability of either stimulating or inhibiting cell growth. Among them, 2,836 (6,958 clones) were known genes, 372 (384 clones) were previously unrecognized genes, and 598 (895 clones) were unigenes of uncharacterized structure and function. A comprehensive analysis of the genes and the potential mechanisms for their involvement in the regulation of cell growth is provided. The genes were classified into four categories: I, genes related to the basic cellular mechanism for growth and survival; II, genes related to the cellular microenvironment; III, genes related to host-cell systemic regulation; and IV, genes of miscellaneous function. The extensive growth-regulatory activity of genes with such highly diversified functions suggests that cancer may be related to multiple levels of cellular and systemic controls. The present assay provides a direct genomewide functional screening method. It offers a better understanding of the basic machinery of oncogenesis, including previously undescribed systemic regulatory mechanisms, and also provides a tool for gene discovery with potential clinical applications

Ultraviolet photoemission spectra of Yb 2.75 C 60 thin films are measured. The valence band is a wide hump centered at ϳ0.8 eV below the Fermi level. The result also indicates the semiconducting property of Yb 2.75 C 60 since no Fermi edge is observed. The hybridization between 6s states of Yb and the lowest-unoccupiedmolecular-orbital ͑LUMO͒ band of C 60 is non-negligible although it should not be considered to be strong. More than 14% of Yb 6s electrons are estimated to be distributed in the covalent bonds between Yb and C 60 . The spectra for submonolayer C 60 on Yb film reveal that Yb 6s electrons can easily transfer to C 60 and such demonstrate that the bonding in Yb 2.75 C 60 is mainly ionic. The LUMOϩ1 orbital of the submonolayer C 60 is partially occupied, which is different from the case in Yb 2.75 C 60 . There is no evidence of trivalent Yb in the spectra.

The effect of C 60 molecular rotation on the nanotribological properties of C 60 single crystal surfaces has been studied by atomic/frictional force microscopy. The orientational order-disorder phase transition, in which the high temperature C 60 free rotation is reduced to a low temperature hindered rotation, is shown to give rise to an abrupt change in friction and adhesion. This change in frictional force is quantitatively consistent with the observed change in adhesion. The similar slopes of the friction versus load curves in both phases indicate that the friction coefficient in the two phases remains about the same. Hence the C 60 rotation does not provide an additional energy dissipation channel in the friction process. DOI: 10.1103/PhysRevLett.90.146102 PACS numbers: 68.35.Af, 61.48.+c, 64.70.Kb, 68.35.Np C 60 molecules are near-perfect spheres [1]. Soon after the discovery of C 60 , there was speculation about the unique lubrication properties of C 60 films due to the spherical shape of the individual molecules [2][3][4][5]. According to classical mechanics, spherical balls between two moving bodies can act as a lubricant by the exploitation of low rolling friction [6]. In analogy, C 60 molecules were anticipated as nanoscale ball bearings to act as a good lubricant, but this expectation was not borne out by either microscopic or macroscopic experiments [2 -5,7-10]. The best friction result between two C 60 films has a friction coefficient of 0:15, much larger than that of graphite (0.01) [11].In this Letter, we report the role of C 60 rotation on nanotribological properties. The rotational degree of freedom of the C 60 molecules in crystalline C 60 provides a good system to study the mechanism of energy dissipation during frictional processes, which is the central question for tribological studies [12]. At room temperature, the crystalline C 60 has a face-centered cubic (fcc) structure [13]. In each cubic unit cell, there are four molecules and each molecule rotates (nearly) freely at a very high frequency ( 10 11 Hz) [13,14]. Since each C 60 molecule is constantly changing its orientation, all molecules are equivalent when measured over a time period longer than the rotational period. After cooling down to 260 K, the crystal undergoes a first-order orientational order-disorder phase transition from an fcc to a simple cubic (sc) structure [13,15]. In the sc phase, the lattice constant is smaller by 0:34% [16], which corresponds to a change in molecular orientation [15]. All the C 60 balls retain their former lattice positions in the newly contracted fcc arrangement, but the four C 60 molecules associated with the primitive cubic cell are no longer equivalent because they adopt their own specific orientations along different h111i directions [13]. The C 60 molecules now execute a hindered rotation (jump reorientation between symmetrically equivalent orientations) at a much slower speed [13,15].Previous studies on the frictional properties of C 60 were mostly done with C 60 thin film samples, prepared...