50 research outputs found
Dam methylase from Escherichia coli: kinetic studies using modified DNA oligomers: hemimethylated substrates.
We have measured steady-state kinetics of the N6-adenine methyltransferase Dam Mtase using as substrates non-selfcomplementary tetradecamer duplexs (d[GCCGGATCTAGACG]-d[CGTCTAGATCC-GGC]) containing the hemimethylated GATC target sequence in one or the other strand and modifications in the GATC target sequence of the complementary strands. Modifications included substitution of guanine by hypoxanthine (I), thymine by uracil (U) or 5-ethyl-uracil (E) and adenine by 2,6-diamino-purine (D). Thermodynamic parameters were obtained from the concentration dependence of the melting temperature (Tm) of the duplexes. Large differences in DNA methylation of duplexes containing single dI for dG substitution of the Dam recognition site were observed compared with the canonical substrate, if the substitution involved the top strand (on the G.C rich side). Substitution in either strand by uracil (dU) or 5-ethyluracil (dE) resulted in small perturbation of the methylation patterns. When 2,6-diamino-purine (dD) replaced the adenine to be methylated, small, but significant methylation was observed. The kinetic parameters of the methylation reaction were compared with the thermodynamic free energies and significant correlation was observed
Hyperfine interaction with the Th nucleus and its low-lying isomeric state
The thorium nucleus with mass number has attracted much interest
because its extremely low lying first excited isomeric state at about eV
opens the possibility for the development of a nuclear clock. However, neither
the exact energy of this nuclear isomer nor properties, such as nuclear
magnetic dipole and electric quadrupole moment are known to a high precision so
far. The latter can be determined by investigating the hyperfine structure of
thorium atoms or ions. Due to its electronic structure and the long lifetime of
the nuclear isomeric state, Th is especially suitable for such kind of
studies. In this letter we present a combined experimental and theoretical
investigation of the hyperfine structure of the Th ion in the
nuclear ground and isomeric state. A very good agreement between theory and
experiment is found for the nuclear ground state. Moreover, we use our
calculations to confirm the recently presented experimental value for the
nuclear magnetic dipole moment of the thorium nuclear isomer, which was in
contradiction to previous theoretical studies