Relationship between yeast polyribosomes and Upf proteins required for nonsense mRNA decay.

In yeast, the accelerated rate of decay of nonsense mutant mRNAs, called nonsense-mediated mRNA decay, requires three proteins, Upf1p, Upf2p, and Upf3p. Single, double, and triple disruptions of the UPF genes had nearly identical effects on nonsense mRNA accumulation, suggesting that the encoded proteins function in a common pathway. We examined the distribution of epitope-tagged versions of Upf proteins by sucrose density gradient fractionation of soluble lysates and found that all three proteins co-distributed with 80 S ribosomal particles and polyribosomes. Treatment of lysates with RNase A caused a coincident collapse of polyribosomes and each Upf protein into fractions containing 80 S ribosomal particles, as expected for proteins that are associated with polyribosomes. Mutations in the cysteine-rich (zinc finger) and RNA helicase domains of Upf1p caused loss of function, but the mutant proteins remained polyribosome-associated. Density gradient profiles for Upf1p were unchanged in the absence of Upf3p, and although similar, were modestly shifted to fractions lighter than those containing polyribosomes in the absence of Upf2p. Upf2p shifted toward heavier polyribosome fractions in the absence of Upf1p and into fractions containing 80 S particles and lighter fractions in the absence of Upf3p. Our results suggest that the association of Upf2p with polyribosomes typically found in a wild-type strain depends on the presence and opposing effects of Upf1p and Upf3p.

Derailment: success and failure.

Today's career executive faces the challenges of the health care industry and the challenges of managing one's own career. The ability to accurately assess one's own career and use that knowledge to plan future career strategies is essential. This article gives many practical hints for career success.

MR imaging of excessively obese patients: the use of an open permanent magnet.

Excessive obesity can pose a limitation to both clinical and radiographic evaluation. Although CT and MR have revolutionized head and body imaging, patients with weights above 300 lb present a restriction of these imaging modalities. Magnetic resonance imaging (MRI) is well suited for imaging excessively obese patients, because the RF used does not have difficulty in penetrating large amounts of adipose tissue as ionizing radiation or sound waves does. The limitations of conventional MR imaging in these obese patients are the gantry size and the table weight limit. The recent development of a new low field MR imager with a larger gantry size and greater weight capacity, has the potential for imaging obese patients that cannot be evaluated by standard CT or MR. In this paper, we report our experience in imaging nine excessively obese patients with weights between 350 and 490 lb using a permanent magnet operating at 0.064 T.