Molecular Machines That Control Genes  What new Howard Hughes
Medical Institute president Robert Tijan said about the
activities of our genes in 1995: They are tightly regulated by
elaborate complexes of proteins that assemble on DNA.
Perturbations in the normal operation of these assemblies can
lead to disease  Editor's Note: This article was originally
published in the February 1995 issue of Scientific American. We
are reposting it this week because Robert Tijan has just been
named president of the Howard Hughes Medical Institute.  Asthma,
cancer, heart disease, immune disorders and viral infections are
seemingly disparate conditions. Yet they turn out to share a
surprising feature. All arise to a great extent from
overproduction or underproduction of one or more proteins, the
molecules that carry out most reactions in the body. This
realization has recently lent new urgency to research aimed at
understanding, and ultimately manipulating, the fascinating
biochemical machinery that regulates an essential ste