Structural comparisons of mouse histones 2A.X and 2A.Z with 2A.1 and 2A.2

The tryptic peptide patterns of the recently described H2A species H2A.X and H2A.Z from mouse were compared with the tryptic peptide patterns of the major mouse H2A's, H2A.1 and H2A.2. The identities of the H2A.1 peptides were determined by comparing their in vivo labeling with various 14C-labeled amino acids with the expected labeling determined from the known sequence. All the H2A.1 tryptic peptides larger than dipeptides were accounted for. The procedure was repeated for H2A.2, H2A.X and H2A.Z. H2A.X was found to have large regions of sequence identical to that of H2A.1 with the variability occurring mainly near the N and C termini. Mouse H2A.X had some sequence characteristics found in the sequenced H2A's of trout and sea urchin. In contrast, H2A.Z was found to have only two peptides in common with H2A.1; in addition, the labeling patterns of the non-identical peptides were too different to suggest analogous peptides. We conclude from these studies that H2A.Z differs considerably from H2A.1 in major portions of its sequence.     

Conformational analysis of canonical 2-deoxyribonucleotides. 2. Purine nucleotides

The molecular structure of different conformers of isolated canonical purine 2'-deoxyribonucleotides 2-deoxyadenosine-5'-phosphate (pdA) and 2'-deoxyguanosine-5'-phosphate (pdG) was optimized using the B3LYP/6-31G(d) method. The results of the calculations reveal that the geometrical parameters and relative stability of the conformers significantly depend on the nature of the nucleobase, its orientation, the conformation of the furanose ring, the charge of the phosphate group and the character of the intramolecular hydrogen bonds. Analysis of the electron density distribution in purine nucleotides reveals the existence of a number of intramolecular hydrogen bonds. In general, the south conformer has a lower energy at the anti orientation of the base, and both conformers occur as the most stable for the syn orientation of the nucleobases. The results of the calculations reveal that the geometry and relative energy of the conformers of purine DNTs may be easily tuned by the charge of the phosphate group.     

Polynucleotides. XL. Synthesis and properties of poly 2''-azido-2''-deoxyadenylic acid.

Poly 2'-azido-2'-deoxyadenylic acid (Poly Az) was synthesized from 2'-azido-2'-deoxyadenosine diphosphate by polynucleotide phosphorylase. Poly (Az) has U.V. absorption properties similar to poly (A) and hypochromicity of 40% at 0.1 M Na+ and neutrality. CD curve also resembled to that of poly (A), but has smaller ellipticity. Titration of poly (Az) with HCl gave a transition at pH 5.5, but exact structure of the acid-form complex was not elucidated. Upon mixing with poly (U), poly (Az) forms a 1:1 and 1:2 complexes having Tm's somewhat higher than that of poly (A)- poly (U) complex in the same condition.     

Analysis of permethylated hexopyranosyl-2-acetamido-2-deoxyhexitols by g.l.c.-m.s.

The major product obtained on acetonation of d-mannose with a 2-molar excess of isopropenyl methyl (or ethyl) ether is 4,6-O-isopropylidene-α-d-mannopyranose (3a), the product of kinetic acetonation: a larger excess of the reagent leads, to the 2,3:4,6-diisopropylidene acetal (6). The course of the reaction and side-products formed were examined in detail. The 1,2,3-triacetate of 3a was deacetonated to give α-d-mannopyranose 1,2,3-triacetate; similar reactions were performed on the β anomers. The 1-acetate of the diacetal 6 could be selectively deacetonated to give 1-O-acetyl-2,3-O-isopropylidene-α-d-mannopyranose. The reactions provide access to protected derivatives of d-mannose, and partially acylated derivatives, having modes of substitution different from those obtainable by classical acetonation procedures conducted under conditions of thermodynamic control.     

Synthesis of p-nitrophenyl 2-acetamido-2-deoxy-O-beta-D-galactopyranosyl-beta-D-glucopyranosides.

Reaction of p-nitrophenyl 2-acetamido-2-deoxy-4,6-O-(p-methoxybenzylidene)-beta-D-glucopyranoside (2) with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide (3) under the usual conditions, followed by removal of the p-methoxybenzylidene group and O-deacylation, produced crystalline p-nitrophenyl 2-acetamido-2-deoxy-3-O-beta-D-galactopyranosyl-beta-D-glucopyranoside (6). Starting from p-nitrophenyl 2-acetamido 3,4-di-O-acetyl-2-deoxy-beta-D-glucopyranoside, the synthesis of p-nitrophenyl 2-acetamido-2-deoxy-6-O-beta-D-galactopyranosyl-beta-D-glucopyranoside was also accomplished.     

Zur Planktonkunde Spitzbergens. 2.

Ohne Zusammenfassung     

Preparation of 2''-thio-2''-deoxycytidine 2'':3''-phosphorothioate.

The synthesis of a novel ribonucleotide analog 2'-thio-2' deoxycytidine 2':3'-O,S-phosphorothioate is described. In the first step, 2,2'-anhydro 1-beta-D-arabinosylcytosine was thiophosphorylated by the action of dithiophosphate, a process which gave predominantly the 3'-O-phosphorothioate isomer. An intramolecular displacement reaction led to the formation of the title compound. Structure and reactivity of this thioanalog differ substantially from 2':3'-CMP.