SCIENCE
NEWS
This Week
Fiji
Australia
“the main problem” with some other long-term studies is the rarity of reported predator attacks. —S. MILIUS
Nearly Naked
New Zealand
Large swath of Pacific
lacks seafloor sediment
South Pacific
Bare Zone
BARE FACTS A 2-million-square-kilometer region (orange) is almost devoid of seafloor sediment.
Oceanographers have discovered a broad,
almost-bare patch of seafloor in the remote
South Pacific. An unusual combination of
circumstances has left the region without
the mineral and organic sediments hundreds
of meters deep that are typical elsewhere in
the world’s oceans, the scientists say.
The sediment-poor region is about the
size of the Mediterranean Sea and centered
approximately 4,000 kilometers east of
New Zealand. Researchers discovered the
area, which they dubbed the South Pacific
Bare Zone, during a cruise early last year,
says David K. Rea, a marine geologist at the
University of Michigan in Ann Arbor.
The scientists were surprised when their
seismic equipment, which detects sediment
only when it’s at least 5 meters thick, indicated that there was no sediment in that
region. The team then sent sampling equipment more than 4 km to the seafloor and
discovered as little as 50 centimeters of sediment in some places.
A unique combination of factors seems
to have dictated the area’s dearth of sediment that’s accumulated since the basalt
crust below formed between 85 million and
34 million years ago, Rea and his colleagues
report in the October Geology.
First, the area has nutrient-poor surface
waters and so is home to few organisms.
Therefore, there aren’t large quantities of
plankton to die, fall to the bottom, and accumulate, as they do in seas with high biological content, says Rea.
Second, the deepest waters in this area
contain less carbonate and silica than those
in other locations do, so skeletons of organisms that reach the seafloor dissolve.
Third, the bare zone is far from any major
landmass, so little windblown dust ends up
in the surface waters and eventually sinks.
Finally, the region has little if any hydrothermal activity to spew water containing dissolved minerals that would precipitate.
Rea says that he and his colleagues had
expected to find at least a dozen meters of
sediment in the region. “It’s fun to be wrong
sometimes,” he notes.
Neil C. Mitchell, a marine geologist at
Cardiff University in Wales, suggests
another factor that may contribute to the
sediment skimpiness of the area. It’s out of
the path of major ocean currents, so Antarctic icebergs carrying material scraped from
that continent don’t pass over the bare zone
and drop sediment, says Mitchell.
The sparse sediments may permit
researchers to find seafloor substances that
are typically hidden, says David Scholl, a
marine geologist at Stanford University. For
instance, meteor dust, which falls evenly
over Earth’s surface, may be more easily
detectable in the bare zone than elsewhere,
says Scholl. —S. PERKINS
Pretty
in Pictures
Details of molecular
machinery gain Nobel
In yeast, the enzyme that transcribes the
protein-making instructions encoded in
DNA consists of roughly 30,000 atoms.
Five years ago, Roger D. Kornberg published a solo portrait and an action shot of
this molecular machinery in atomic detail.
Last week, Kornberg, of the Stanford University School of Medicine, was awarded the
2006 Nobel Prize in Chemistry for those
images, which were the product of nearly
2 decades of research in his laboratory on the
enzyme called RNA polymerase.
Working out the structure of RNA polymerase was “a marvelous achievement,” says
James T. Kadonaga, a biochemist at the
University of California, San Diego. “It’s one
piece of a much larger puzzle, but an
extremely important piece.”
The structure of RNA polymerase
intrigued Kornberg because this enzyme
begins the protein-making process. It
copies gene sequences from DNA to create a single-stranded nucleic acid called
messenger RNA. Other parts of the cell
then use the messenger RNA to direct protein assembly.
To determine the enzyme’s structure,
Kornberg and his colleagues used RNA
polymerase from yeast cells. One of the
many challenges in their work, says Kornberg, was developing the procedures to
grow sufficient quantities of pure, three-dimensional crystals of RNA polymerase,
which is a complex of 12 proteins.
Advances in X-ray crystallography, which
the team used to image the enzyme, were
also critical. In this technique, a sample
scatters X rays that researchers had focused
on it. From characteristics of the scatter, a
computer creates an image showing the
positions of the structure’s atoms.
The work of Kornberg’s team culminated in 2001 with two publications, one
showing inactive RNA polymerase and the
other capturing the machinery during the
transcription process. The latter image
shows how RNA polymerase grasps DNA
and how the enzyme chooses the correct
building blocks for the messenger RNA.
It’s a picture that “I regard as one of the
most indelible of our work,” says Kornberg.
Jeremy M. Berg, director of the National
Institute of General Medical Sciences in
Bethesda, Md., says, “If you understand
the structure and the mechanism of how
RNA polymerase works, it will help you
understand gene regulation,” which in turn
is “hugely important” to studies of disease.
The work by Kornberg and others has
provided “significant” insights, says
Richard H. Ebright of Rutgers University
in Piscataway, N.J. He adds, “Most people
in our field imagined [a Nobel prize on
transcription] would be shared.”
“Transcription is a very large field,” says
Kadonaga. “While I’m really happy for Roger
[Kornberg], I also hope there is a place for
other people, like Robert Roeder” of Rockefeller University in New York City, who discovered that there are multiple forms of RNA
polymerase. “They are very deserving,”
Kadonaga says. —A. CUNNINGHAM
E. ROELL
