Word: khorana
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Like the sages of his native India, Organic Chemist and Nobel Laureate* Har Gobind Khorana is an extremely patient man. Nine years ago, he began working on the chemical synthesis of a single gene-the basic unit of heredity. By 1970 he had constructed a yeast-cell gene identical to the original-except for one thing: it lacked the vital "start" and "stop" signals to make it function in a living cell. Last week members of Khorana's team at the Massachusetts Institute of Technology disclosed that his goal had finally been achieved. At an American Chemical Society meeting...
Like Beads. Khorana's creation is a duplicate of one of the thousands of genes in the spiral-staircase structure of the DNA molecule in the common intestinal bacterium E. coli. Unlike human genes, which include millions of chemical "steps" along much larger DNA molecules, this bacterial gene contains only 199 full steps, each a pair of letters in the genetic code. Consisting of chemicals called nucleotides, these letters make up words in the gene's message-in this case, instructions to transfer the amino acid tyrosine to the cell's protein-manufacturing centers...
Duplicating the gene's basic structure, which had been determined earlier by British researchers, was extremely tedious, trial-and-error work. Each scientist on Khorana's team was assigned to assemble 1% segments of DNA. This involved chemically linking one nucleotide to another, like beads of a necklace, until a chain ten to 12 nucleotides long had been created. Eventually the team built up 40 segments, all of them single stranded. These had to be paired to form double-stranded DNA segments that had to be connected end to end in proper sequence to duplicate the bacterial gene...
Unlike other experiments in "genetic engineering" (TIME, July 19), Khorana's work apparently does not pose dangers. For one thing, the gene is assembled with control signals, which enables scientists to prevent runaway activity. Also, there is no attempt to produce new gene combinations from different organisms that could accidentally breed mutants against which humans or other life have no natural defenses. Indeed, some scientists see in gene synthesis enormous potential for good. It could, for example, eventually be used to replace defective genes in ailing humans-in hemophiliacs, say. It may also bring new understanding-and possibly control...
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...