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The telomere complex must allow nucleases and helicases to process chromosome ends to make them substrates for telomerase, while preventing these same activities from disrupting chromosome end-protection. Replication protein A (RPA) binds to single-stranded DNA and is required for DNA replication, recombination, repair, and telomere maintenance. In fission yeast, the telomere binding protein Taz1 protects telomeres and negatively regulates telomerase. Here, we show that taz1-d rad11-D223Y double mutants lose their telomeric DNA, indicating that RPA (Rad11) and Taz1 are synergistically required to prevent telomere loss. Telomere loss in the taz1-d rad11-D223Y double mutants was suppressed by additional mutation of the helicase domain in a RecQ helicase (Rqh1), or by overexpression of Pot1, a single-strand telomere binding protein that is essential for protection of chromosome ends. From our results, we propose that in the absence of Taz1 and functional RPA, Pot1 cannot function properly and the helicase activity of Rqh1 promotes telomere loss. Our results suggest that controlling the activity of Rqh1 at telomeres is critical for the prevention of genomic instability.

The telomere complex must allow nucleases and helicases to process chromosome ends to make them substrates for telomerase, while preventing these same activities from disrupting chromosome end-protection. Replication protein A (RPA) binds to single-stranded DNA and is required for DNA replication, recombination, repair, and telomere maintenance. In fission yeast, the telomere binding protein Taz1 protects telomeres and negatively regulates telomerase. Here, we show that taz1-d rad11-D223Ydouble mutants lose their telomeric DNA, indicating that RPA (Rad11) and Taz1 are synergistically required to prevent telomere loss. Telomere loss in the taz1-d rad11-D223Ydouble mutants was suppressed by additional mutation of the helicase domain in a RecQ helicase (Rqh1), or by overexpression of Pot1, a single-strand telomere binding protein that is essential for protection of chromosome ends. From our results, we propose that in the absence of Taz1 and functional RPA, Pot1 cannot function properly and the helicase activity of Rqh1 promotes telomere loss. Our results suggest that controlling the activity of Rqh1 at telomeres is critical for the prevention of genomic instability.

The iron mixed-valence complex, (n-C3H7)4N[FeIIFeIII(dto)3] (dto = dithiooxalato) shows a charge-transfer (CT) phase transition at TCT = 122.4 K. In the vicinity of TCT, the spin state changes from FeII (S = 2) – FeIII (S = 1/2) (high-temperature phase: HTP) to FeII (S = 0) – FeIII (S = 5/2) (low-temperature phase: LTP) accompanied by a charge transfer between FeII and FeIII. This complex also undergoes a ferromagnetic transition at 7 K in the LTP. In order to investigate the mechanism of the CT phase transition and the ferromagnetism, we have systematically synthesized (n-CnH2n+1)4N[FeIIFeIII(dto)3] (n = 3–6), and have investigated their physical properties by magnetic susceptibility, powder X-ray diffraction measurements, and ESR spectroscopy. The compounds (n-CnH2n+1)4N[FeIIFeIII(dto)3] (n = 3–6) display ferromagnetic phase transitions at 7 K, 7 K (& 13 K), 19.5 K, and 22 K, respectively. For n = 3 and 4, the CT phase transitions take place at TCT ≈ 120 K and TCT ≈ 140 K, respectively. For n = 5 and 6, on the other hand, the CT phase transition does not occur, and the spin configuration of FeII (S = 2) and FeIII (S = 1/2) corresponding to the HTP for n = 3 and 4 is stable between 2 K and 300 K. The cation size of (n-CnH2n+1)4N+ (n = 3–6) acts as an effective internal pressure which induces the CT phase transition and the ferromagnetic ordering in the [FeIIFeIII(dto)3]–∞ layer. We also discuss the mechanism of the CT phase transition and the ferromagnetism induced by the charge-transfer interaction between FeII and FeIII. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

We have synthesized and investigated the physical properties of a new mixed valence iron complex, ( n -C 3 H 7 ) 4 N[Fe II Fe III (mto) 3 ] (mto=C 2 O 3 S). This complex behaves as a ferrimagnet with T N =38 K and θ= m 117 K. From the analysis of the Mössbauer spectrum of ( n -C 3 H 7 ) 4 N[Fe II Fe III (mto) 3 ] at 298 K, the spin state of Fe II was determined to be the high spin state (S=2), but it was difficult to determine the spin state of Fe III . So that, in order to elucidate the spin state of Fe III , we have investigated ESR spectra, and confirmed the coexistence of high spin state (S=5/2) and low spin state (S=1/2) for the Fe III sites. Moreover, we have synthesized ( n -C 4 H 9 ) 4 N[Fe II Fe III (mto) 3 ]. This complex shows the ferrimagnetic phase transition at 41 K, and Weiss constant is m 76 K. In our previous paper, we have reported that mixed-valence complex ( n -C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ] (dto=C 2 O 2 S 2 ) shows a new type of phase transition connected with charge transfer phase transition and spin-crossover transition around 120 K. In the title complexes, the charge transfer phase transition was not observed. mixed valence complex charge transfer phase transition monothiooxalato

We have investigated the physical properties of (n-C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](dto = C 2 O 2 S 2 ) by means of 57 Fe Mössbauer spectroscopy, magnetic susceptibility, and ESR. From the analysis of 57 Fe Mössbauer spectra and ESR signal, we have discovered a new type of first order phase transition around 120 K for (n-C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](n = 3, 4), where the charge transfer transition between Fe II and Fe III occurs reversibly. In the higher temperature phase, the Fe III ( S = 1/2) and Fe II ( S = 2) sites are coordinated by six S atoms and six O atoms, respectively. In the lower temperature phase, on the other hand, the Fe III ( S = 5/2) and Fe II ( S = 0) sites are coordinated by six O atoms and six S atoms, respectively. Moreover, we have found the ferromagnetic phase transition in this system. The ferromagnetic order is induced by the charge transfer interaction between the Fe III ( S = 5/2) and Fe II ( S = 0) sites. spin crossover ferromagnetism charge transfer phase transition mixed valence

We have investigated the spin-crossover behavior for one-dimensional complexes [Fe(trz) 3 (RSO 3 ) 2 (trz= triazole) and two-dimensional mixed-valence complexes (C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](dto=C 2 O 2 S 2 ). For the case of [Fe(4-NH 2 trz) 3 ](RSO 3 ) 2 , we have controlled Tc and the thermal hysteresis width of spin transition by using the isomerization of counter anion or the fastener effect between the alkyl chains of counter anions C n H 2n+1 SO 3 − . Moreover, we have synthesized a [Fe(Htrz) 3 ] film by using an ion-exchange film having SO 3 − , which shows the spin transition around room temperature. For the case of (C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](n=3,4), we have found a charge transfer phase transition between Fe II and Fe III around 120 K.

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Not a classical spin‐crossover: The heat capacity of the mixed‐valence complex {[(n‐C3H7)4N][FeIIFeIII(dto)3]}∞(dto=dithiooxalato, see scheme) exhibits a phase transition at 122.4 K as a result of electron transfer, and gives insight into the cooperative phenomena exhibited by the multifunctional material.

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We have synthesized [FeII(H-trz)3]ncomplex film by using ion-exchange resin(Nafion) as counter anion, and have found the spin crossover phenomenon about at 260 K. Moreover, we have proved the existence of straight one-dimensional Fe chain structure of [FeII(H-trz)3]non Nafion by means of EXAFS.