The effects of monovalent (Na+, K+) and diva- lent (Mg2+, Ca2+, Mn2+) ions on the interaction between DNA and histone are studied using the molecular combing tech- nique. ?-DNA molecules and DNA-histone complexes incu- bated with metal cations (Na+, K+, Mg2+, Ca2+, Mn2+) are stretched on hydrophobic surfaces, and directly observed by fluorescence microscopy. The results indicate that when these cations are added into the DNA solution, the fluorescence intensities of the stained DNA are reduced differently. The monovalent cations (Na+, K+) inhibit binding of histone to DNA. The divalent cations (Mg2+, Ca2+, Mn2+) enhance sig- nificantly the binding of histone to DNA and the binding of the DNA-histone complex to the hydrophobic surface. Mn2+ also induces condensation and aggregation of the DNA- his- tone complex.
A fluctuating ratchet model of non-Markov process is presented to describe the processive movement of molecular motors of single-headed kinesin KIF1A, where the fluctuation perturbation to the local potential is introduced and the detailed ATPase pathway of the motor is included. The theoretical results show good quantitative agreement with the previous experimental ones.
The effects of divalent ions(Mn2+,Mg2+,Ca2+) on the interaction between DNA and histone are studied using a fluorescence anisotropy assay. Fluorescence anisotropies of DNA and DNA-histone in the presence of divalent ions(Mn2+,Mg2+,Ca2+) are measured. The results indicate that histone reduces the fluorescence anisotropy of lambda DNA while the divalent ions(Mn2+,Mg2+,Ca2+) significantly enhance the fluorescence anisotropy. Compared to the case of DNA incubated with histone alone,there are more histones binding to DNA when divalent ion,histone and DNA are incubated together. We also find that Mn2+ makes the DNA-histone complexes more condensed than the other ions do.
LIU YuYingWANG PengYeDOU ShuoXingXIE PingXI XuGuang
ATP synthase is a rotary motor which is composed of two portions： the ‘rotor＇ Fo, consisting of a c-ring, and the ‘stator＇ F1, consisting of an a3/33 hexamer. In different species, the number of c-subunits which form the c-ring is varied from 10 to 14, whereas the a3/33 hexamer is fixed to be 3-fold symmetrical. We have numerically studied the rotational coupling between Fo with varied number of c-subunits and F1. It is found that, for any number of c-subunits, the rotor Fo advances 3 steps per revolution on average, which is determined by the period of F1, whereas the exact angular pausing positions are determined by the period of Fo. When the symmetry of the c-ring of Fo is matched with the 3-fold symmetry of F1, the three steps have equivalent sizes. If not matched, the three steps become nonequivalent： both the step size and average dwell time are different for these steps.
