The Changes of Phenotypic and Gene Frequencies of Esterase-D Isozyme in Japanese Quail by Full-sib Mating

本研究は,全きょうだい交配によって近交世代を進めた場合の日本ウズラのエステラーゼDアイソザイムの表現型頻度と遺伝子頻度の変化について検討した. 材料は当研究室で無作為交配によって維持した閉鎖集団から作出した近交群と無作為交配群である. これらの交配群から得た成雌雄ウズラの血球エステラーゼDアイソザイムがデンプンゲル電気泳動法により検出された. 得られた結果は要約すると以下の通りである. 1.系統数,家系数は近交群では1世代目38系統38家系で出発したが,近交世代に伴い急激に減少し,5世代目では3系統12家系となった. これに対して,無作為交配群では40家系が維持された. 2.近交群では,FF型の表現型頻度は4世代まで近交世代に伴い徐々に増加する傾向がみられた. FS型の表現型頻度は2世代までは近交に伴い急激な減少がみられたが,その後の世代では増加する傾向が認められた. またSS型の表現型頻度は近交に伴いわずかに増加する傾向がみられたが,3代以降の世代では減少した. これに対して,無作為交配群では世代に伴う変化は認められなかった. 3.近交群では,Es-DFの遺伝子頻度は2世代目0.307から3世代目0.458となり,2世代から3世代目にかけて増加した. 一方Es-Dsの遺伝子頻度は2世代目0.693から3世代目0.542となり,3世代目では減少した. これに対して,無作為交配群ではいずれの遺伝子頻度も世代に伴う著しい変化は認められなかった. 4.近交群では,FF型の観察値は4世代まで期待値と適合した. またFS型とSS型の観察値は2世代までは期待値と適合したが,それ以後の世代では適合しなかった. これに対して,無作為交配群では観察値と期待値は適合した. 5.近交群では,生存系統が絶滅系統に比較してFS型のヘテロ接合体頻度は高く,一方SS型のホモ接合体頻度は低くなる傾向がみられた. 6.以上の結果から,日本ウズラにおいて近交世代を進めた場合エステラーゼDのヘテロ接合体はホモ接合体に比べて有利であること,および近交退化は遺伝子のホモ接合体の増加とポリジーン系のヘテロ性の低下に起因することが示唆された

Direct Observation of Strand Passage by DNA-Topoisomerase and Its Limited Processivity

Type-II DNA topoisomerases resolve DNA entanglements such as supercoils, knots and catenanes by passing one segment of DNA duplex through a transient enzyme-bridged double-stranded break in another segment. The ATP-dependent passage reaction has previously been demonstrated at the single-molecule level, showing apparent processivity at saturating ATP. Here we directly observed the strand passage by human topoisomerase IIα, after winding a pair of fluorescently stained DNA molecules with optical tweezers for 30 turns into an X-shaped braid. On average 0.51±0.33 µm (11±6 turns) of a braid was unlinked in a burst of reactions taking 8±4 s, the unlinked length being essentially independent of the enzyme concentration between 0.25–37 pM. The time elapsed before the start of processive unlinking decreased with the enzyme concentration, being ∼100 s at 3.7 pM. These results are consistent with a scenario where the enzyme binds to one DNA for a period of ∼10 s, waiting for multiple diffusional encounters with the other DNA to transport it across the break ∼10 times, and then dissociates from the binding site without waiting for the exhaustion of transportable DNA segments

Radiosensitization Effect of Gold Nanoparticles on Plasmid DNA Damage Induced by Therapeutic MV X-rays

Gold nanoparticles (AuNPs) can be used with megavolt (MV) X-rays to exert radiosensitization effects, as demonstrated in cell survival assays and mouse experiments. However, the detailed mechanisms are not clear; besides physical dose enhancement, several chemical and biological processes have been proposed. Reducing the AuNP concentration while achieving sufficient enhancement is necessary for the clinical application of AuNPs. Here, we used positively charged (+) AuNPs to determine the radiosensitization effects of AuNPs combined with MV X-rays on DNA damage in vitro. We examined the effect of low concentrations of AuNPs on DNA damage and reactive oxygen species (ROS) generation. DNA damage was promoted by 1.4 nm +AuNP with dose enhancement factors of 1.4 ± 0.2 for single-strand breaks and 1.2 ± 0.1 for double-strand breaks. +AuNPs combined with MV X-rays induced radiosensitization at the DNA level, indicating that the effects were physical and/or chemical. Although −AuNPs induced similar ROS levels, they did not cause considerable DNA damage. Thus, dose enhancement by low concentrations of +AuNPs may have occurred with the increase in the local +AuNP concentration around DNA or via DNA binding. +AuNPs showed stronger radiosensitization effects than −AuNPs. Combining +AuNPs with MV X-rays in radiation therapy may improve clinical outcomes

Carbon Dioxide Adsorption onto Polyethylenimine-Functionalized Porous Chitosan Beads

Polyethylenimine-functionalized porous chitosan (PEI–CS) beads were prepared and their CO₂ adsorption performance was evaluated. The CO₂ adsorption capacity of PEI–CS was dependent upon both the amine content and surface area of the functionalized beads. PEI–CS showed a CO₂ adsorption capacity of 2.3 mmol/g at 313 K and 15 kPa of CO₂ in the absence of water vapor that considerably increased to 3.6 mmol/g in the presence of water vapor. To rationalize this phenomenon, the CO₂ adsorption mechanisms in the absence and presence of water vapor were investigated by diffuse reflectance infrared Fourier transform spectroscopy. The results indicated that the mechanism of CO₂ adsorption onto PEI–CS, in both the absence and presence of water vapor, involved the formation of carbamate. Therefore, the higher CO₂ adsorption capacity in the presence of water vapor was attributed to the increased accessibility to amino groups of PEI–CS, owing to swelling of the polyethylenimine chain and/or chitosan framework upon adsorption of water. The herein reported chitosan-based material displays high CO₂ adsorption capacity as well as excellent regenerability and, thereby, shows potential as an adsorbent for CO₂ capture

Direct Observation of Strand Passage by DNA- Topoisomerase and Its Limited Processivity

Abstract Type-II DNA topoisomerases resolve DNA entanglements such as supercoils, knots and catenanes by passing one segment of DNA duplex through a transient enzyme-bridged double-stranded break in another segment. The ATP-dependent passage reaction has previously been demonstrated at the single-molecule level, showing apparent processivity at saturating ATP. Here we directly observed the strand passage by human topoisomerase IIa, after winding a pair of fluorescently stained DNA molecules with optical tweezers for 30 turns into an X-shaped braid. On average 0.5160.33 mm (1166 turns) of a braid was unlinked in a burst of reactions taking 864 s, the unlinked length being essentially independent of the enzyme concentration between 0.25-37 pM. The time elapsed before the start of processive unlinking decreased with the enzyme concentration, being ,100 s at 3.7 pM. These results are consistent with a scenario where the enzyme binds to one DNA for a period of ,10 s, waiting for multiple diffusional encounters with the other DNA to transport it across the break ,10 times, and then dissociates from the binding site without waiting for the exhaustion of transportable DNA segments