No abstract

Increasingly detailed structural and dynamic studies are highlighting the precision with which biomolecules execute often complex tasks at the molecular scale. The efficiency and versatility of these processes have inspired many attempts to mimic or harness them. To date, biomolecules have been used to perform computational operations and actuation, to construct artificial transcriptional loops that behave like simple circuit elements and to direct the assembly of nanocrystals. Further development of these approaches requires new tools for the physical and chemical manipulation of biological systems. Biomolecular activity has been triggered optically through the use of chromophores, but direct electronic control over biomolecular 'machinery' in a specific and fully reversible manner has not yet been achieved. Here we demonstrate remote electronic control over the hybridization behaviour of DNA molecules, by inductive coupling of a radio-frequency magnetic field to a metal nanocrystal covalently linked to DNA. Inductive coupling to the nanocrystal increases the local temperature of the bound DNA, thereby inducing denaturation while leaving surrounding molecules relatively unaffected. Moreover, because dissolved biomolecules dissipate heat in less than 50 picoseconds (ref. 16), the switching is fully reversible. Inductive heating of macroscopic samples is widely used, but the present approach should allow extension of this concept to the control of hybridization and thus of a broad range of biological functions on the molecular scale.

The 3-O-sulfation of glucosamine residues is an important modification during the biosynthesis of heparan sulfate (HS). Our previous studies have led us to purify and molecularly clone the heparan sulfate D-glucosaminyl 3-O-sulfotransferase (3-OST-1), which is the key enzyme converting nonanticoagulant heparan sulfate (HS inact ) to anticoagulant heparan sulfate (HS act ). In this study, we expressed and characterized the fulllength cDNAs of 3-OST-1 homologous genes, designated as 3-OST-2, 3-OST-3 A , and 3-OST-3 B as described in the accompanying paper ( 35 S]HS suggested that 3-OST-2 transfers sulfate to GlcA2S-GlcNS and IdoA2S-GlcNS; 3-OST-3 A transfers sulfate to IdoA2S-GlcNS. Our results demonstrate that the 3-O-sulfation of glucosamine is generated by different isoforms depending on the saccharide structures around the modified glucosamine residue. This discovery has provided evidence for a new cellular mechanism for generating a defined saccharide sequence in structurally complex HS polysaccharide.

Lyme disease is the most common vector-borne disease in the United States. The causative agent is the spirochete Borrelia burgdorferi. The copy number and organization of the genes encoding the rRNAs of this organism were determined. There is a single gene for 16S rRNA and two copies each of the 23S rRNA and 5S rRNA genes. All of the genes are located within a chromosomal fragment of approximately 9.5 to 10.0 kb. The 23S and 5S rRNA genes are tandemly duplicated in the order 23S-5S-23S-5S and are apparently not linked to the 16S rRNA gene, which is situated over 2 kb upstream from the 23S-5S duplication. The individual copies of the 23S-5S duplication are separated by a 182-bp spacer. Within each 23S-5S unit, an identical 22-bp spacer separates the 23S and 5S rRNA sequences from each other. The genome organization of the 23S-5S gene cluster in a number of different B. burgdorferi isolates obtained at a number of different geographical locations, as well as in several other species of Borrelia, was investigated. All isolates of B. burgdorferi tested displayed the tandem duplication, whereas the closely related species B. hermsii, B. anserina, and B. turicatae all contained a single copy of each of the genes. In addition, different geographical isolates of B. burgdorferi can be differentiated on the basis of a restriction fragment length polymorphism associated with the 23S-5S gene cluster. This polymorphism can be a useful tool for the determination of genetic relatedness between different isolates of B. burgdorferi.

The serine proteases of the intrinsic blood coagulation cascade are slowly neutralized by antithrombin (AT) 1 (reviewed in Ref. 1). This inhibition is secondary to the generation of 1:1 enzyme⅐AT complexes whose formation is dramatically enhanced by the mast cell product, heparin (2). Damus et al. (3) hypothesized that endothelial cell surface heparan sulfate proteoglycans (HSPGs) function in a similar fashion to accelerate coagulation enzyme inactivation by AT and therefore are responsible for the nonthrombogenic properties of blood vessels. We initially demonstrated that perfusion of the hind limbs of normal rodents and rodents deficient in mast cells with purified thrombin and AT leads to a greatly elevated rate of thrombin⅐AT complex formation and that the enzyme heparitinase as well as the natural heparin antagonist platelet factor 4 suppress the above acceleration (4, 5). We subsequently showed that cultured cloned bovine macrovascular and rodent microvascular endothelial cells synthesize both anticoagulant HSPG (HSPG act ) and nonanticoagulant HSPG (HSPG inact ) (6 -8). HSPG act bear glycosaminoglycan (GAG) chains that bind tightly to AT and accelerate thrombin⅐AT complex generation (6 -8).The biosynthesis of HSPG act requires generation of a core protein; assembly of a linkage region of four neutral sugars on specific serine attachment sites of the core protein; elongation of a GAG backbone composed of alternating N-acetylglu-