The 1.3 A crystal structure of a biotin-binding pseudoknot and the basis for RNA molecular recognition.

A pseudoknot-containing aptamer isolated from a pool of random sequence molecules has been shown previously to represent an optimal RNA solution to the problem of binding biotin. The affinity of this RNA molecule is nonetheless orders of magnitude weaker than that of its highly evolved protein analogs, avidin and streptavidin. To understand the structural basis for biotin binding and to compare directly strategies for ligand recognition available to proteins and RNA molecules, we have determined the 1.

The structural basis for molecular recognition by the vitamin B 12 RNA aptamer.

Previous solution structures of ligand-binding RNA aptamers have shown that molecular recognition is achieved by the folding of an initially unstructured RNA around its cognate ligand, coupling the processes of RNA folding and binding. The 3 A crystal structure of the cyanocobalamin (vitamin B12) aptamer reported here suggests a different approach to molecular recognition in which elements of RNA secondary structure combine to create a solvent-accessible docking surface for a large, complex ligand. Central to this structure is a locally folding RNA triplex, stabilized by a novel three-stranded zipper.

Preliminary crystallographic characterization of an in vitro evolved biotin-binding RNA pseudoknot.

A biotin-binding RNA pseudoknot developed through in vitro selection has been crystallized using the hanging-drop vapor-phase diffusion method. The X-ray diffraction data indicate that the crystals belong to the space group P4222 with unit-cell parameters a = b = 55.2, c = 62.

Functional requirements for specific ligand recognition by a biotin-binding RNA pseudoknot.

Ligand-binding RNAs and DNAs (aptamers) isolated by in vitro selection from random sequence pools provide convenient model systems for understanding the basic relationships between RNA structure and function. We describe a series of experiments that define the functional requirements for an RNA motif that specifies high-affinity binding to the carboxylation cofactor biotin. A simple pseudoknot containing an adenosine-rich loop accounts for binding in all independently derived aptamers selected to bind biotin, suggesting that it alone represents a global optimum for recognition of this particular nonaromatic, electrostatically neutral ligand.

Expression of hepatic metallothionein messenger RNA in feral and caged fish species correlates with muscle mercury levels.

Metallothioneins (MTs) are low-molecular-weight cytosolic proteins that are induced by cellular stress as well as exposure to various heavy metals including mercury. Excessive residues of mercury have recently been identified in various fish species of the lower Ouachita River system in Arkansas. Fillets of mature largemouth bass (Micropterus salmoides) collected from Woodard Lake, an ox-bow lake of the Ouachita River, possessed muscle residues of mercury ranging from 0.

Mapping of the trifunctional fatty acid synthetase gene FAS2 on chromosome XVI of Saccharomyces cerevisiae.

The trifunctional FAS2 gene encoding subunit alpha of the Saccharomyces cerevisiae fatty acid synthetase complex was mapped on the left arm of chromosome XVI 24 centimorgans proximal to GAL4 and 39 centimorgans distal to PEP4 relative to the centromere. Mapping was achieved by three independent methods: meiotic co-segregation of FAS2 and ARO7 in recombination-deficient spo11-mutants: tetrad analysis of crosses between FAS2, GAL4 and PEP4; and Southern hybridization of purified FAS2 DNA with individual yeast chromosomes separated by pulsed-field gel electrophoresis.

Short-term nursing therapy: a conceptual model for inpatient psychiatric care.

As a result of changing perspectives in psychiatric practice and increasing fiscal limits imposed by legislative and economic issues, psychiatric nurses have found their traditional models of practice challenged by shortened lengths of stay and the need for more efficient assessment and treatment. Short-term nursing therapy, which draws on the principles of crisis intervention and brief psychotherapy, was developed to provide psychiatric nurses with a cohesive, comprehensive nursing philosophy for practical application in changing inpatient settings. The authors review the development of the short-term nursing therapy concept from the perspective of the changing inpatient milieu and nurse-patient relationship.

Reproductive performance and profitability of heifers fed to weigh 272 or 318 kg at the start of the first breeding season.

Reproductive performance and weaning weight of the first calf was determined in 221 Brahman crossbred heifers fed to weigh either 272 (TW1) or 318 kg (TW2) at the start of their first breeding season (target weight). Heifers were divided into light- (below average) and heavyweight (above average) groups on the basis of initial weight. Within each target weight, heifers were fed in three lots.