"The discovery is important not only because there is a new way to intervene in HIV infection but there is also a sense that we have suddenly got some insight into a potential role for what have previously been very mysterious cell components," Dr Joseph Sodroski said in an interview Wednesday.

The protein, called Trim5-alpha, prevents HIV from shedding a protective coating and inserting its genetic material into the infected cell, combining with the cell's own DNA. If the virus does not complete this integration process relatively quickly it decays and becomes non-infectious.

Trim5-alpha is a very specific inhibitor of HIV. Sodroski and his colleagues believe its potency may differ in individuals, which could explain why some people infected with the virus proceed to AIDS more quickly than others. It may also be possible for scientists to find a way to increase its potency.

The researchers also suspect it could be the first of more Trim proteins in humans which determine the susceptibility of cells to viruses and other infectious agents.

"We may be tapping into a system of innate or intrinsic resistance to viruses," added Sodroski, who reported the finding in the science journal Nature.

If a treatment targeting the protein is developed, the researchers envision it being used along with existing AIDS drugs that work at different points in the replication process.

"It could be used in various settings," said Sodroski.

Possible examples could be to stop someone exposed to the virus from becoming infected or to limit the ability of the virus to infect new cells in someone who is already HIV positive.

"Identification of this HIV-blocking factor opens new avenues for intervening in the early stage of HIV infection, before the virus can gain a toehold," Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID) in the United States which supported the research, said in a statement.

"Basic discoveries like this provide the scientific springboard to future improvements in therapies for HIV disease," he added.

"This sale has attracted all types from large international wholesalers to a couple of eternal optimists," said Balix Manxgaba, group director of Auction Alliance, which is handling sealed bids for the surplus stock.

The condom factory was built as a joint venture as part of a complex arms purchase deal which saw South Africa award Germany a $594 million (318 million pounds) contract to build submarines.

Its construction was hailed in a country with the world's biggest HIV/AIDS caseload.

But the factory never opened, and now its remaining stock is up for sale. For the man who thinks even bigger, the condom factory itself will be up for sale next month.

WASHINGTON (AFP) - Sexually transmitted diseases mainly affect 15 to 24 year olds in the United States, amounting to nine million cases a year, according to a study.

While the age group accounts for only one quarter of sexually active people, those affected represent half of all cases of STDs.

Human papillomavirus (HPV), trichomoniasis and chlamydia are the three diseases that affect nine in 10 of all new cases of STD infections in the group, US journal Perspectives in Sexual and Reproductive Health said.

"It is not surprising that teens and young adults contract a disproportionate number of infections," noted Sharon Camp of the Alan Guttmacher Institute which financed the study.

"Most young people are sexually active, and many are ill equipped to prevent STDs or seek testing and treatment," Camp said.

New estimates suggest that the direct medical costs associated with a lifetime of treating cases of STD infection diagnosed in young people in 2000 could reach 6.5 billion dollars. Ninety percent of that cost however is due to treatment of HIV/AIDS, and the small percentage of cases that result in cervical abnormalities or genital warts.

The authors of the study, published in the January/February edition of the journal, emphasize prevention and education to cut the future cost of STD infections.

"Investing money today in STD prevention and education could dramatically reduce the incidence of these infections, and thus future treatment costs," the authors said

Adolescents "need realistic sex education that teaches them how to prevent STDs and unwanted pregnancies," Camp said.

"It is essential to have medically accurate information about condoms and other contraceptive methods, and guidance in how to access appropriate prevention, testing and treatment services."

A number of STD prevention programs in American schools, financed by the public purse and by conservative organizations, try and teach sexual abstinence, without mentioning condoms to prevent disease in the event of sexual relations.