Highly efficient copying of single-stranded DNA by eukaryotic cell chromatin.

Chromatin prepared from S phase hepatoma tissue culture (HTC) cell incorporates in vitro about 11-14 pmoles [3H]dTMP into DNA in 30 min. Single-stranded DNA added to this chromatin stimulates DNA synthesis more than 40-fold whereas activated DNA enhances it about 60-fold. By contrast, stimulation of DNA synthesis by activated DNA in a crude nuclear extract exceeds the stimulation exerted by denatured DNA by a factor of 7. Stimulation of DNA synthesis by denatured DNA is not due to stabilization of either the chromatin or the product of the endogenous reaction. On the other hand, we find that poly(dC) and poly (dT) enhance DNA synthesis by serving as templates which are copied by chromatin in a true complementary fashion. It seems therefore, that eukaryotic cell chromatin is able to copy single-stranded DNA at a high efficiency. Chromatin of G1 arrested cell copies exogenous templates at a considerably reduced rate. The enzyme responsible for the copying of denatured DNA is tentatively identified as DNA polymerase alpha on the basis of its sensitivity to sulfhydril group blocking, its requirements for ions and failure to copy the ribo strand of oligo(dT) poly(A)

A structural investigation of the coordination behaviour of 4,6-dimethylpyrimidine-2-thiol with Zinc (II) at pH 6-A zwitterionic complex exhibiting unusual ZnS3N2 chromophore in solid state

Complexation between Zn2+ and 4,6-dimethylpyrimidine-2-thiol was attempted with ZnO, ZnSO4 and Zn(OAc)(2) In all cases, the same compound, tris-4,6-dimethylpyrimidine-2-thiolato zinc (II) was generated without anion incorporation It crystallized from methanol in the space group P2(1)/a. Z = 4 The molecular structure exemplifies an uncommon coordination of 3 ligands to Zn(II) through their thiolate centres: one of the ligands is protonated to effectively form a zwitterionic complex, which exhibits capped rectangular pyramidal coordination geometry of an anionic ZnN2S3 chromophore. In crystalline state. the ligand moieties differ in respect of orientations and interactions while in solution they behave as identical components of a symmetric molecule The crystal structure is stabilized by pi stacking and periodic H-bonding interactions along a. The presence of a protonated azomethine N in one ol the ligands is confirmed from the high conductance and acidic pH of an aqueous methanolic solution of the complex (C) 2009 Elsevier B V All rights reserve

Molecular mechanics-assisted crystal engineering of solid state photoreactions: application to the Yang photocyclization of a-1-norbornylacetophenone derivatives.

Based on mol. mechanics, Yang photocyclization of a-1-norbornylacetophenone derivs. in the cryst. state was engineered through methylation adjacent to the carbonyl group, thus changing the conformation in the crystal and leading to enhanced diastereo- and enantioselectivity