IN THIS ISSUE . . .
June 20, 2006
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featured in this digest. Although only the lead scientists
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Cool Image: Gene Silencing
Pretty in pink, the enzyme histone deacetylase (HDA6) stands
out against a background of blue-tinted DNA in the nucleus
of an Arabidopsis plant cell. Here, HDA6 concentrates
in the nucleolus (top center), where ribosomal RNA genes reside.
The enzyme, known to switch off certain genes, silences the
ribosomal RNA genes from one parent while those from the other
parent remain active. This chromosome-specific silencing of
ribosomal RNA genes is an unusual phenomenon observed in hybrid
plants. Courtesy of Olga Pontes and Craig Pikaard, geneticists
at Washington University in St. Louis.
Good News for Grapefruit Juice Drinkers
Caption: Grapefruits and juice. Courtesy of Monika Adamczyk.
Unlike other citrus juices, a single glass of grapefruit
juice can alter blood levels of drugs used to treat certain
conditions like high blood pressure or high cholesterol. This
effect stems from an interaction between the juice and an
enzyme in the intestines, which normally chews up drugs as
our bodies try to absorb them. But when grapefruit juice interacts
with the enzyme, more of the drug gets in the bloodstream,
causing potentially undesirable and even dangerous side effects.
Now, pharmacologist Paul Watkins of the University of the
North Carolina at Chapel Hill School of Medicine has identified
the chemical furanocoumarin as the active ingredient in grapefruit
that causes this effect. The finding could lead to a juice
lacking this chemical and to the identification of other food
products with similar drug interactions.
lab home page
abstract (from the May 2006 issue of The American Journal
of Clinical Nutrition)
Tracking Genetic Variation
helix and Etruscan funerary statue. Courtesy of Elise
Human population genetics research can shed light on the
genetic variation between individuals and the evolutionary
processes that give rise to that variation. Researchers collaborating
on a population genetics project have produced a computational
model of modern human evolution that can be used to test a
range of hypotheses related to demographics and genetic diversity.
Anthropologist Joanna Mountain of Stanford University, working
with Guido Barbujani of the University of Ferrara in Italy,
used the model to rule out a genetic link between contemporary
Tuscans and the ancient Etruscans, a people that inhabited
Tuscany centuries ago. The findings challenge the common assumption
that current inhabitants of a region are descended from earlier
residents and are helping scientists understand the origin
of patterns of genetic variation observed today.
lab home page (no longer available)
abstract (from the May 23, 2006, issue of PNAS)
Making Sense of Cilia
Chlamydomonas reinhardtii, a green alga.
Courtesy of DOE Joint Genome Institute.
A simple green alga that lives in small ponds and puddles
may hold secrets about human health and disease. That’s
according to William Snell, a cell biologist at the University
of Texas Southwestern Medical Center, who studies the microscopic
hairs called cilia that help the organism move and mate.
In humans, cilia play a role in the sense of smell, brain
development, kidney function, and many other activities.
Now, Snell has identified a biochemical process that cilia
on the alga use to send signals. His work could shed light
on other functions of cilia in humans, some of which remain
unknown. Since defective cilia can lead to human disorders,
such as kidney disease, the work also may set the stage
for drug discovery.
abstract (from May 5, 2006, issue of Cell)
Neutrons Offer Insights into Proteins
diagram of the atomic arrangement in the active site
of the enzyme D-xylose isomerase. Courtesy of Bunick.
The same technique that can detect moisture in the wings
of jet fighter planes has shown its strength in determining
the shapes of proteins. A team of researchers, including structural
biologist Gerard Bunick of the University of Tennessee, used
neutrons to locate hydrogen atoms in the active site of D-xylose
isomerase—an enzyme that serves as a model for understanding
other types of proteins and as a catalyst for making commercial
products, such high-fructose corn syrup and ethanol. Typically,
hydrogen atoms make up about half of all the atoms in a protein
and play a key role in protein function. Because other protein
determination techniques, such as X-ray crystallography, do
not adequately capture the location of hydrogen atoms, the
neutron approach offers a complementary strategy that could
speed drug discovery and improve medicines.
Chase home page
abstract (from the May 30, 2006, issue of PNAS)