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The ability of MutS to recognize mismatched DNA is required to initiate a mismatch repair (MMR) system. ATP binding and hydrolysis are essential in this process, but their role in MMR is still not fully understood. In this study, steady-state ATPase activities of MutS from Escherichia coli were investigated using the spectrophotometric method with a double end-blocked heteroduplex containing gapped bases. The ATPase activities of MutS increased as the number of gapped bases increased in a double end-blocked heteroduplex with 2-8 gapped bases in the chain, indicating that MutS dissociates from DNA when it reaches a scission during movement along the DNA. Since movement of MutS along the chain does not require extensive ATP hydrolysis and the ATPase activity is only enhanced when MutS dissociates from a heteroduplex, these results support the sliding clamp model in which ATP binding by MutS induces the formation of a hydrolysis-independent sliding clamp.

To study the effect of sequence on DNA structure, the two decamer crystal structures one alternating, d(GTACGCGTAC), and the other non-alternating, d(GGCCGCGGCC), were solved. Crystals of both decamers belong to the hexagonal space group P6 1 22, with one strand in the asymmetric unit. The unit cell constants of the alternating decamer are a = b = 39.26 A, c = 77.70 A. The structure was refined with 1,828 reflections from 8.0 to 2.0 A resolution to an R value of 21.3% with all DNA atoms and 63 water molecules. The isomorphous non-alternating decamer had unit cell dimensions of a = b = 39.05 A, c = 82.15 A. The structure was refined with 2,423 reflections from 8.0 to 2.0 A resolution to a final R value of 22.2% for all DNA atoms and 65 water molecules. Although the average helical parameters of the decamers are typical of A-DNAs, there are some minor differences between them. The helical twist, rise, x-displacement, inclination and roll alternate in the alternating decamer, but do not in the non-alternating decamer. The backbone conformations in both structures show some differences; the residue G(7) of the alternating decamer is trans for a and ywhile the trans conformations are observed at the residue G(8) of the non-alternating decamer.

Excitation and emission spectra and luminescence lifetimes of Eu3+ complexes obtained by dissolving anhydrous EuCl3 and EuCl3/2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (Bis-tris) in anhydrous dimethylformamide (DMF) and those from a Eu(Bis-tris)2Cl3 crystalline sample have been studied. Two distinct Eu3+ complexes were observed when anhydrous EuCl3 was dissolved in anhydrous DMF, and one was interpreted as an outer-sphere complex of Cl− anion. Dissolution of an excess amount of vacuum dried NaClO4 or KPF6 in anhydrous DMF resulted in longer luminescence lifetimes, presumably reducing the effects of trace amounts of water in the solvent due to competitive binding of the water in the solvent by alkali metal cations. The quenching rate constant for the 5D0 state of Eu3+ ion by each complexed DMF molecule in solution and by each OH group in the Bis-tris from the Eu(Bis-tris)2Cl3 crystalline sample were 54 ± 1 and 495 ± 5 s−1, respectively, and these were used to interpret the plausible structures of the different Eu3+ complexes in the EuCl3/Bis-tris/DMF solution.

We have synthesized novel fluorophores by using Sonogashira reactions of 1,4-bis(dibromovinyl)benzene and 2,5-bis(dibromovinyl)thiophene with various aromatic bromides. The emission maxima of these fluorophores vary from the indigo blue to the reddish-orange region, depending on the structures of aromatic nuclei and peripheral moieties.

The effect of wild-type and mutant MutL on the steady-state ATPase activity of MutS from Escherichia coli has been investigated in the absence and presence of 22, 50, and 75 base pair hetero- and homoduplex DNAs with open and blocked ends. The steady-state ATPase activity of MutS has been measured at 37 degrees C using a spectrophotometric method. The presence of MutL did not affect appreciably on the ATPase activity of MutS in the absence of DNA or in the presence of blocked end homoduplex DNAs. However, the addition of MutL affected oppositely on the ATPase activity of MutS in the presence of G-T mismatched DNAs depending on their end status. We have also found that only the ATPase active forms of MutL increased the ATPase activity of MutS in the presence of G-T mismatched DNAs with blocked ends. The results suggest that MutL ATPase activity is required to catalyze dissociation of the MutS sliding clamps.

We have synthesized a family of bis-enediynes by two complementary Pd/Cu-catalyzed Sonogashira cross-coupling methods. One is a modified Sonogashira reaction between the TMS-protected tetraalkyne 20 (or 21) and various aromatic bromides to afford bis-enediynes 22a-d and 23a-d bearing different peripheral aryl units. The other, the reaction of bifunctional 1,1-dibromo-1-alkenes with phenylacetylene, afforded a series of bis-enediynes 24-32 bearing various core aryl groups. These chemical modifications to the core and periphery of bis-enediynes induce dramatic changes in absorption and emission spectra. Bis-enediynes 22 and 23 show a large Stokes shift of about 50-110 nm when compared to the less-conjugated bis-enediynes 20 and 21. Absorptions and emissions of bis-enediynes 25, 27-29, and 31 were red-shifted relative to those of enediyne 35. Substantial increases in fluorescence quantum yields are observed as a result of extending the pi-conjugation. The emission wavelength of bis-enediynes was tailored from indigo blue to reddish-orange, suggesting that the color of emission can be tunable by modification of the core and/or peripheral units.

A new class of fluorescence sensors for ammonium and organoammonium ions has been disclosed. One of the sensors, an alaninol-derived tripodal oxazoline (1a) shows significant fluorescence enhancement upon binding NH(4)(+) but little response toward K(+), Na(+), and Mg(2+) ions. Owing to its chiral environment, a phenylglycinol-derived tripodal oxazoline (1b) shows chiral discrimination in fluorescence upon binding enantiomeric guests. [reaction: see text]

A commonly used buffer, 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (Bis-Tris) coordinates lanthanide(III) ion strongly in water to form molecular species that are highly active for the hydrolysis of a phosphate diester, bis(4-nitrophenyl) phosphate.