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Nonsense Mutations in the Chlamydomonas Chloroplast Gene That Codes for the Large Subunit of Ribulosebisphosphate Carboxylase/Oxygenase

Robert J. Spreitzer, Michel Goldschmidt-Clermont, Michele Rahire and Jean-David Rochaix
Proceedings of the National Academy of Sciences of the United States of America
Vol. 82, No. 16 (Aug. 15, 1985), pp. 5460-5464
Stable URL: http://www.jstor.org/stable/25671
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Nonsense Mutations in the Chlamydomonas Chloroplast Gene That Codes for the Large Subunit of Ribulosebisphosphate Carboxylase/Oxygenase
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Abstract

The Chlamydomonas reinhardtii chloroplast mutants 18-5B and 18-7G lack both the chloroplast-encoded large subunit and nuclear-encoded small subunit of the chloroplast enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39). A chloroplast intergenic-suppression model has been postulated to account for the genetic instability of 18-5B revertants. Here, we have determined the molecular basis of the 18-5B and 18-7G mutants. They contain nonsense mutations close to the 3′ and 5′ ends of their large-subunit genes, respectively. Pulse-chase experiments revealed that the 18-5B mutant produces a truncated large subunit that is unstable. In connection with previous experiments, this work identifies nonsense suppression in the chloroplast. Small subunits are also synthesized but then degraded in the mutants. Thus, the coordinated absence of subunits is achieved through degradation of the small subunit in the specific absence of the large subunit.

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