The IRA1 gene is a negative regulator of the RAS-cyclic AMP pathway in Saccharomyces cerevisiae. To identify other genes involved in this pathway, we screened yeast genomic DNA libraries for genes that can suppress the heat shock sensitivity of the ira1 mutation on a multicopy vector. We identified IRA2, encoding a protein of 3,079 amino acids, that is 45% identical to the IRA1 protein. The region homologous between the IRA1 protein and ras GTPase-activating protein is also conserved in IRA2. IRA2 maps 11 centimorgans distal to the arg1 locus on the left arm of chromosome XV and was found to be allelic to glc4. Disruption of the IRA2 gene resulted in (i) increased sensitivity to heat shock and nitrogen starvation, (ii) sporulation defects, and (iii) suppression of the lethality of the cdc25 mutant. Analysis of disruption mutants of IRA1 and IRA2 indicated that IRA1 and IRA2 proteins additively regulate the RAS-cyclic AMP pathway in a negative fashion. Expression of the IRA2 domain homologous with GAP is sufficient for complementation of the heat shock sensitivity of ira2, suggesting that IRA down regulates RAS activity by stimulating the GTPase activity of RAS proteins.

The combined scanning tunneling microscopy/spectroscopy (STM/STS) and the break-junction tunneling spectroscopy (BJTS) measurements of the three-layered Pb x Bi2-x Sr2Ca2Cu3O10+y cuprate superconductors were carried out. The averaged dI/dV spectrum obtained by the STS shows the gap Δ STS ≈ 45 meV, while that of BJTS shows Δ BJ ≈ 35 meV. In case of the BJTS measurements, we also referred the zero bias (ZB) peak as being due to the maximum Josephson current IJc . The product of IJc and normal resistance RN (IJcRN ) was obtained IJcRN ≈ 3.5 mV at T = 11 K, which is one order lower than that of the BCS-based Ambegaokar-Baratoff theory with Δ BJ =35 meV taken into account. With increasing the temperature, the IJcRN was reduced and vanished just below the Tc (≈ 106 K), indicating the bulk superconductivity. Simultaneously, from the temperature dependence of the gap features from 80 K to 120 K, the gap Δ was shown to persist across the Tc , indicating that the IJcRN product is a significant parameter for understanding the cuprate superconductivity.

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The scanning tunnel microscopy/scanning tunnel spectroscopy (STM/STS) measurements of the local quasiparticle density of states (LDOS) in Cu x -Fe1.01-x Se0.4Te0.6 (x = 0.01-0.03) superconductors were carried out. Critical temperatures Tc decrease with increasing Cu-impurity doping level x. STM images show clear regular square arrangements of spots with the lattice spacing ~ 0.38 nm as well as the randomly distributed large spots, which are most possibly due to excess Fe atoms. While the STM image resembles that of non-doped Fe(Se,Te), the LDOS map shows various extra spot structures with bright (with higher magnitudes of dI/dV) and dark (with lower magnitudes of dI/dV) regions. With increasing x, the number of such spots grows proportionally, indicating that these spots most probably correspond to the dopant Cu atoms.

Scanning tunneling microscopy and spectroscopy (STM/STS) and break-junction tunnel spectroscopy (B.TTS) measurements are performed on the pristine layered α-TiNCl semiconductor (pri-TiNCl), being the precursor of superconducting nitride chlorides. The STM topography of pri-TiNCl shows basic crystal structures with the lattice periods of a0≈ 0.38 nm and b0≈ 0.31 nm, ensuring that a clean a–b surface of micro-single crystals is obtained. From the STS measurements, the averaged conductance versus voltage dependence dI/dV(V) reveals kink structures at relatively high bias voltages of |F| ∼ −50 mV and −100 mV. The spatial (r-) conductance distributions dI/dV (V, r) (dI/dV maps) proportional to those of quasiparticle local densities of states (LDOSes) exhibit the bias-independent streak structures with the period of (4.8 ± 0.2) b0, which are predominantly observed within the range of |V| < 95 mV. The temperature dependence of the dI/dV B.TTS spectra shows the gap structure with the energy scale of 4Σ = 180 meV vanishing at Ts ∼ 120 K. Thus, the ratio of the gap Σ to the transition temperature Ts is 2Σ/kBTs ∼ 10. Here, kB is the Boltzmann constant. Such a ratio is typical of the pseudogap features in cuprate superconductors and dielectric gap characteristics in layered chalcogenides with charge-density waves.