Wataru Tanaka

Active optics experiments with a 62-cm thin mirror

An engineering prototype with a 62 cm thin meniscus mirror to investigate the practical problems of the JNLT active optics system has been constructed. The structure and the performance of the prototype and the basis for the control algorithms are described. The stiffness of the mirror and the purity of figure control for the correction of lower order Zernike modes were measured for this system. The results of experiments to control the surface figure of the mirror under varying elevation angle of the telescope or under external force load are reported. The thermal effects on this system were also evaluated.

Evidence for DNA Cleavage Caused Directly by a transfer RNA-Targeting Toxin

The killer yeast species Pichia acaciae produces a heteromeric killer protein, PaT, that causes DNA damage and arrests the cell cycle of sensitive Saccharomyces cerevisiae in the S phase. However, the mechanism by which DNA damage occurs remains elusive. A previous study has indicated that Orf2p, a subunit of PaT, specifically cleaves an anticodon loop of an S. cerevisiae transfer RNA (tRNAGln mcm5s2UUG). This finding raised a question about whether the DNA damage is a result of the tRNA cleavage or whether Orf2p directly associates with and cleaves the genomic DNA of sensitive yeast cells. We showed that Orf2p cleaves genomic DNA in addition to cleaving tRNA in vitro. This DNA cleavage requires the same Orf2p residue as that needed for tRNA cleavage, His299. The expression of Orf2p, in which His299 was substituted to alanine, abolished the cell cycle arrest of the host cell. Moreover, the translation impairment induced by tRNA cleavage enabled Orf2p to enter the nucleus, thereby inducing histone phosphorylation.

Altitude variation of ultraviolet oxygen night airglow

Night airglow of oxygen 130.4 and 135.6 nm emissions was measured by a spectrophotometer aborad an S520 sounding rocket, launched at 19:50 JST (10:50 UT) on 14 February, 1982 from Kagoshima, Japan. The altitude variation of the emissions was obtained from 110 to 266 km at zenith angles of 35.5°±4°. The emission intensity around 260 km was about 160R and is roughly compatible with model calculations taking account of O++e− radiative recombination as well as O+−O− mutual neutralization. Some excess of about 50R, compared to the model calculation, was observed around 200 km. Possible explanations of the excess are: (i) remnant oxygen ions during the transition period from day to night and (ii) diffuse radiation from the background sky. Model calculations taking account of remnant oxygen ions were also performed by adding an excess electron density to the original density profile. However, it was found that an unreasonably large electron density is required around 200 km (∼5×105 cm−3) to produce the observed intensity. It is also probable that some contribution from the background sky is present in the observed intensity.