A DOMINANT MUTATION IN THE CHLAMYDOMONAS-REINHARDTII NUCLEAR GENE SIM30 SUPPRESSES TRANSLATIONAL DEFECTS CAUSED BY INITIATION CODON MUTATIONS IN CHLOROPLAST GENES

A suppressor of a translation initiation defect caused by an AUG, to A UU mutation in the Chlamydomonas reinhardtii chloroplast petD gene was isolated, defining a nuclear locus that we have named SIM30. A domina nt mutant allele at this locus, sim30-1d, was found to increase the tr anslation initiation rate of the mutant petD mRNA, sim30-1d was also a ble to suppress the translational defect caused by an AUG to AUC mutat ion in the petD gene, and AUG to AUU mutation in die chloroplast petA gene. We therefore suggest that the SIM30 gene may encode a general ch loroplast translation factor. The ability of sim30-1d to suppress the petD AUG to AUU mutation is diminished in the presence of one or more antibiotic resistance markers located within the 16S and 23S rRNAs, su ggesting that the activity of the sim30-1d gene product in translation initiation may involve interaction with ribosomal subunits.