Base excision repair in the thermophile Thermus sp. strain X-1.

The thermophile Thermus sp. strain X-1, grown at 70 degrees C, contains uracil-DNA glycosylase and apurinic endonuclease activities, both of which are known to have roles in the repair of DNA damaged by heat. Both of these activities have temperature optima of about 70 degrees C. However, neither of these activities is present in quantities significantly greater than that found in Escherichia coli grown at 37 degrees C. Therefore, it appears that thermophilic organisms may not contain greatly elevated levels of the enzymes thought to be involved in the repair of DNA damaged by heat.     

Mechanical Operation and Intersubunit Coordination of Ring-Shaped Molecular Motors: Insights from Single-Molecule Studies

Ring NTPases represent a large and diverse group of proteins that couple their nucleotide hydrolysis activity to a mechanical task involving force generation and some type of transport process in the cell. Because of their shape, these enzymes often operate as gates that separate distinct cellular compartments to control and regulate the passage of chemical species across them. In this manner, ions and small molecules are moved across membranes, biopolymer substrates are segregated between cells or moved into confined spaces, double-stranded nucleic acids are separated into single strands to provide access to the genetic information, and polypeptides are unfolded and processed for recycling. Here we review the recent advances in the characterization of these motors using single-molecule manipulation and detection approaches. We describe the various mechanisms by which ring motors convert chemical energy to mechanical force or torque and coordinate the activities of individual subunits that constitute the ring. We also examine how single-molecule studies have contributed to a better understanding of the structural elements involved in motor-substrate interaction, mechanochemical coupling, and intersubunit coordination. Finally, we discuss how these molecular motors tailor their operation—often through regulation by other cofactors—to suit their unique biological functions.     

Cadmium-containing granules in kidney tissue of the Atlantic white-sided dolphin (Lagenorhyncusacutus) off the Faroe Islands

Top predators from the northern sub-polar and polar areas exhibit high cadmium concentrations in their tissues. In the aim to reveal possible adverse effects, samples of five Atlantic white-sided dolphins Lagenorhyncusacutus have been collected on the occasion of the drive fishery in the Faroe Islands, for ultrastructural investigations and energy dispersive X-ray microanalyses. Cadmium concentrations were less than the limit of detection in both immature individuals and ranged from 22.7 to 31.1 μg g^?1 wet weight in the mature individuals. Two individuals with the highest cadmium concentrations exhibited electron dense mineral concretions in the basal membranes of the proximal tubules. They are spherocrystals made up of numerous strata mineral deposit of calcium and phosphorus together with cadmium. Cadmium has been detected with a molar ratio of Ca:Cd of 10:1 in the middle of these concretions. To our knowledge, this is the first report of such granules in a wild vertebrate. The role of these granules in the detoxification of the metal and the possible pathological effects are considered.     

Partial Purification and Characterization of Uracil-DNA Glycosylase Activity from Chloroplasts of Zea mays Seedlings

A uracil-DNA glycosylase activity has been purified about 750-fold from the chloroplasts of light-grown Zea mays seedlings. This report represents the first direct demonstration of a DNA-glycosylase repair activity in chloroplasts. The activity, in part, was associated with a chloroplast Triton X-100 sensitive membrane. Its apparent K_m was 1.0 micromolar for a poly(dA-dT/U) substrate, and its molecular weight, as determined by gel filtration, was 18,000. The enzyme exhibited optimal activity at pH 7.0 with an atypically narrow pH tolerance. Activity was inhibited greater than 60% by 10 millimolar NaCl, 5 millimolar MgCl₂, or 5 millimolar EDTA. Enzyme activity was inhibited 80% by 10 millimolar N-ethylmaleimide, a sulfhydryl group-blocking agent. The activity removed uracil more rapidly from single-stranded DNA than from double-stranded DNA. With this report, uracil-DNA glycosylase activity has now been attributed to all three DNA-containing organelles of eucaryotic cells.