SCIENCE

But once in a while, Rafflesia does something extraordinary: Out of practically nothing, it creates a monstrous, red-brown flower -- the largest in the world -- as much as three feet in diameter, weighing 15 pounds and with a perfume of rotten flesh.

Because Rafflesia lacks most of the parts that scientists generally rely upon in their classification schemes, botanists have been in the dark about which plants it is related to. Standard DNA analysis has proved fruitless, because in the course of evolving from a free-living ancestor to its current, parasitic form, it gave up many of the genes scientists use for comparison and classification.

Now researchers have at last figured out where Rafflesia belongs in the plant kingdom. Using a subtype of genetic material called mitochondrial DNA, Todd J. Barkman of Western Michigan University and colleagues in Malaysia have come to the unexpected conclusion that Rafflesia is a close cousin of poinsettias, violets and passionflowers. Moreover, they found that a smaller but similar-looking parasitic plant called Mitrastema is not, as suspected, a close relative of Rafflesia but is part of a distant branch of plants that includes rhododendrons and camellias.

That means the two plants came to their similar lifestyles from very different beginnings -- a process called convergent evolution -- the researchers report in the Jan. 8 early edition of the Proceedings of the National Academy of Sciences.

-- Rick Weiss

Bacterial Foe Reveals Methods

When it comes to finding the best way to kill bacteria, consult the experts who have a couple billion years of experience. That is the bright idea a team of scientists in Montreal had in their search for new antibiotics.

Bacteria have their own microbial enemies, called bacteriophages, or just phages. They are viruses that infect a bacteria's single cell and hijack the molecular machinery to make more phages.

The team, led by Jing Liu of the company PhageTech, decided to follow a phage into a bacterial cell to see where it attacked. They assumed that evolution would have favored phages that home in on the most vulnerable parts of the bacterial innards.

They identified 27 phages that kill the bacterium Staphylococcus aureus, a common microbe that causes human illness. They sequenced the phages' genes and tested the product of each gene (usually a protein) to find those that inhibited bacterial growth.

The team studied one protein that did the job particularly well. They discovered that it attached itself to a structure involved in the bacteria's replication, DnaI. This stopped replication of the bacterium, and eventually killed it.

They then screened 125,000 chemical compounds for those that would inhibit the protein-DnaI interaction. They reasoned that when this happened, it might be because the chemical was pushing the phage protein aside and interacting with DnaI itself. They found 11 such compounds.

When they tested two against S. aureus, the compounds killed the bug.

It is not known whether either compound has a future as a drug, but this strategy almost certainly will be used to discover new antimicrobials. It is described in the current issue of the journal Nature Biotechnology.

-- David Brown

Area in Brain, Repression Linked

More than a century ago, Sigmund Freud concluded that painful and undesirable memories can be expunged through a process he called repression. Now researchers using brain imaging techniques have found that people can indeed suppress memories, and they have located the regions of the brain that are involved.

Researchers at the University of Oregon gave subjects pairs of words and then asked them to either recall one of the words or keep it from entering their consciousness for four seconds. Trying to repress the word, they found, made it more difficult to remember it later. In addition, they found that actively suppressing memory made it more difficult to remember information processed just before.

Through the use of functional magnetic resonance imaging, the researchers located which systems and regions of the brain were involved. They found that there was increased activity in the prefrontal sections, indicating that suppression is an active process. Suppressing also reduced activation of the hippocampus, which is associated with memory and recollection.

Their paper, published in the current edition of Science magazine, concludes that "the current findings provide the first neurobiological model of the voluntary form of repression proposed by Freud."

-- Marc Kaufman

A Rafflesia flower in Sabah, Malaysia, is wider than researcher Jamili Nais. The plant has no stem, roots or leaves but produces the world's largest flower.