U.S. scientists have decoded the entire genetic structure of anthrax, a sometimes fatal organism considered a formidable bioterrorist threat. The researchers say the information will help the development of medical defenses against anthrax.

The U.S. government has long listed anthrax as a leading potential bioterrorist weapon. A project to decipher the anthrax genome began with government funding in 1999. But the research suddenly became urgent in late 2001 when someone mailed a powdered form of the bacterium to several U.S. news organizations and politicians. Five people died and 17 others became sick after they inhaled it, and authorities are still searching for the person responsible.

The anthrax gene study is complete. Two separate government-supported private studies have finished reading the anthrax genome and published their results in the journal Nature.

The president of one of the research firms, Claire Fraser of The Institute for Genomic Research near Washington, says the work will make it easier to understand how anthrax causes infection and provide a basis for new drugs and vaccines. Anthrax vaccines exist, but they are not long-lasting.

"We do not know enough about all the mechanisms by which anthrax begins to wreak havoc in its human hosts. If you knew more about how this organism causes disease, you can take a much more informed approach, perhaps developing new antibiotics to target this bacterium specifically, and can greatly accelerate the early phases of new vaccine development," Ms. Fraser said.

Genes are molecules in cells that determine the structure of living things. They produce proteins that carry out basic biological functions. The researchers found a number of genes for proteins that anthrax might need to enter a person's cells. They say these could provide the targets for new drugs.

By comparing the anthrax gene structure against those from two closely-related bacteria, the scientists have found a possible reason anthrax causes a far worse disease. Ms. Fraser's co-researcher, Timothy Read, said it is because anthrax has more genes known to produce lethal poisons.

"We found a number of genes that are not present on its close neighbors. We are not sure whether any of those genes is important in pathogenesis [causing disease], but I think that is a field of study people will now take up," he said.

The other anthrax gene paper in Nature magazine comes from the Chicago biotechnology company Integrated Genomics. Both papers analyze the genetic structure of the so-called Ames strain of anthrax, the one used in the 2001 U.S. postal attacks. But Claire Fraser said that the gene sequences of other strains should be deciphered in order to develop medicines that protect against as many as possible.