RNA is a ubiquitous biopolymer that performs a multitude of essential cellular functions involving the maintenance, transfer, and processing of genetic information. RNA is unique in that it can carry both genetic information and catalytic function. Its secondary structure domains, which fold stably and independently, assemble hierarchically into modular tertiary structures. Studies of these folding events are key to understanding how catalytic RNAs (ribozymes) are able to position reaction components for site-specific chemistry. We have made use of fluorescence techniques to monitor the rates and free energies of folding of the small hairpin and hepatitis delta virus (HDV) ribozymes, found in satellite RNAs of plant and the human hepatitis B viruses, respectively. In particular, fluorescence resonance energy transfer (FRET) has been employed to monitor global conformational changes, and 2-aminopurine fluorescence quenching to probe for local structural rearrangements. In this review we illuminate what we have learned about the reaction pathways of the hairpin and HDV ribozymes, and how our results have complemented other biochemical and biophysical investigations. The structural transitions observed in these two small catalytic RNAs are likely to be found in many other biological RNAs, and the described fluorescence techniques promise to be broadly applicable.

2-Aminopurine↗

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Prion diseases.

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Animals↗

PubMedDate not supplied

Evaluation of infant formula protein quality: comparison of in vitro with in vivo methods.

Two-week protein efficiency ratio (2-wk PER), net protein ratio (NPR), calculated-protein efficiency ratio (C-PER), and discriminant computed-protein efficiency ratio (DC-PER) of milk- and soy-based infant formulas were compared to a 4-week protein efficiency ratio (PER). Expressed relative to ANRC casein, 2-week PER and NPR correlated significantly (P less than 0.01, r = 0.90) with PER. Although C-PER and DC-PER also correlated significantly (P less than 0.01) with PER, r = 0.71 and r = 0.87, respectively, these in vitro methods did not distinguish differences in protein quality among soy-based infant formulas. C-PER and DC-PER, as currently designed, are not applicable to the measurement of protein quality for all types of infant formulas.

Amino Acids↗

PubMedDate not supplied

OSHA noise regulations: pathways to compliance.

Personal ear protection is probably the most expensive and least fruitful approach when one considers the cost of plugs, tests, monitoring and record keeping.

Accident Prevention↗