Stuart Horowitz and Martin A. Gorovsky of the University of Rochester in New York determined the nucleotide (DNA subunit) sequence of two genes in the nuclei of the ciliate. Tetrahymena thermophila. In the standard code, the sequence TAA is a "stop" signal, terminating the translation of a gene. But in these Tetrahymena genes, TAA corresponds to the amino acid glutamine.
Two groups of scientists report in the March 14 NATURE analyses of genes of another ciliate, Paramecium. Francois Caron and Eric Meyer of the National Center of Scientific Research in Gif-sur-Yvette, France, find that both TAA and TAG, which normally terminate gene translation, are scattered through the genes. Analysis of a specific Paramecium gene by J. R. Preer Jr. and colleagues at Indiana University in Bloomington indicates that TAA and TAG code for glutamine. In addition, work in West Germany indicates that TAA encodes glutamine in several genes in another ciliate, Stylonychia. In all these ciliates, only one of the usual stop codons, UGA, appears to act as a termination signal.
Under most conditions, any genetic change involving termination signals is likely to be lethal to an organism. A major puzzle now is how the variation in the genetic code of ciliates could have arisen during evolution.
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|Title Annotation:||genetic coding of ciliates|
|Author:||Miller, Julie Ann|
|Date:||Mar 23, 1985|
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