HIV protein breaks biological clock.

Among the many troubles HIV causes, is apparently a disruption of a person's daily, or circadian, rhythms. "Sleep seems to be a persistent problem" in HIV-infected people, notes John P. Clark of the University of Minnesota at Minneapolis-St. Paul.

The AIDS virus typically infects immune cells, so it hasn't been clear how it might alter the body's biological clock, which is controlled by a brain region called the suprachiasmatic nucleus (SCN). HIV, however, can infect brain cells within as little as a few weeks after a person has contracted the virus.

Clark and his colleagues exposed living slices of SCN tissue from rodents to an HIV protein called Tat and found that the protein altered the slices' circadian rhythm of electrical activity. Researchers used to think that Tat turned on only viral genes needed for HIV to replicate, but they now suspect that the protein is a toxin and may have other roles (SN: 11/6/99, p. 300).

Clark's team also found that live mice getting injections of Tat into their SCNs changed the time of day when they typically run on their exercise wheels. Given these results, the viral protein is probably part of the explanation for the perturbed circadian rhythms of HIV-infected people, Clark concludes.--J.T.