The Gene Makers

Scientists may never be able to emulate Faust's student, Wagner, and create a homunculus, or artificial man. But they seem to be moving steadily closer to the day when they will be able to reproduce the DNA molecule essential to life. Harvard University Biochemists Argiris Efstratiades, Fotis Kafatos, Thomas Maniatis and Allen Maxam report that they have copied a mammalian gene, a unit of the DNA molecule that transmits a specific inherited trait. Their creation: the gene that orders the production of hemoglobin--a blood component--in rabbits.

Five years before the triumph of the Harvard group, Organic Chemist Har Gobind Khorana, a Nobel laureate now working at M.I.T., had synthesized a yeast gene, the simplest gene yet made. Already aware of the sequence of the 77 "code letters," or nucleotides, in the DNA of the gene, Khorana painstakingly "assembled" the letters one at a tune in the proper order to produce a synthetic unit. The rabbit gene is at least eight times as large, containing about 650 nucleotides strung together in a sequence that scientists have not yet completely determined. Clearly the Harvard group could not follow Khorana's route.

Instead, they turned to the research of Nobel Prizewinners Howard Temin and David Baltimore (TIME, July 20, 1970), who had discovered an enzyme, or chemical catalyst, capable of reversing the normal genetic process in which DNA orders the production of "messenger" molecule RNA. Their enzyme permits RNA to manufacture the master molecule DNA. The Harvard team broke down rabbit hemoglobin and isolated its RNA. They then mixed this RNA with the Temin-Baltimore enzyme in a rich nutrient broth. They were thus able to trick the RNA into making the DNA from which it itself had been produced.

Kafatos believes that the artificial gene could be used to make rabbit hemoglobin. But his team is more interested in learning why the sequence of nucleotides in this gene works to order the production of hemoglobin in blood cells but not in other cells. That knowledge would bring scientists still closer to learning the secret of life.

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