Fire killed about 500,000 laboratory mice and injured five people in a blaze at a genetic research center that one lab official said would set back scientific research worldwide. Four construction workers and a firefighter were injured in the midday fire at Jackson Laboratory in Bar Harbor, Me., the world's leading nonprofit supplier of genetically identical mice used in research on cancer, AIDS, diabetes and other human diseases. Kenneth Paigen, the lab's director-designee, said, "We managed to save what are called the foundation stocks . . . the original genetically defined strains." The cause of the fire was under investigation.