title: A nuclear suppressor overcomes defects in the synthesis of the chloroplast psbD gene product caused by mutations in two distinct nuclear genes of Chlamydomonas.
abstract: Mutations in two distinct nuclear genes, called NAC 1 and AC-115, of the unicellular green alga Chlamydomonas reinhardtii cause a specific and dramatic reduction in the synthesis of the chloroplast-encoded D2 polypeptide of Photosystem II. The psbD transcript which encodes the D2 protein is present in the mutant strains, but protein pulse-labeling and immunoprecipitation experiments demonstrate that the synthesis of the D2 protein does not occur normally in these cells. These phenotypes are suppressed by an extragenic nuclear suppressor isolated from a pseudorevertant of a nac 1 mutant. This suppressor is neither allele- nor gene-specific in its suppression and is able to overcome the effects of two different mutations in the NAC 1 gene, as well as a mutation in AC-115. The suppressor seems to be specific in its ability to remedy blocks in psbD mRNA translation in the chloroplast. It is not able to restore the translation of another chloroplast-encoded mRNA which is blocked by another nuclear mutation. The suppressor may identify a new nuclear gene specifically involved in the synthesis of the D2 protein in the chloroplast.
authors.affiliation: Department of Molecular Biology, Lehigh University, Bethlehem, PA 18015, USA.
authors.forename: H Y
authors.initials: HY
authors.lastname: Wu
authors.forename: M R
authors.initials: MR
authors.lastname: Kuchka
mesh_terms: D000818:Animals; D001345:Autoradiography; D015152:Blotting, Northern; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism; D003433:Crosses, Genetic; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis* / Q000235:genetics; D045332:Photosystem II Protein Complex; D011233:Precipitin Tests; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D013489:Suppression, Genetic
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D015800:Protozoan Proteins