SITE-SPECIFIC FACTOR INVOLVED IN THE EDITING OF THE PSBL MESSENGER-RNA IN TOBACCO PLASTIDS

In tobacco plastids, functional psbL mRNA is created by editing an ACG codon to an AUG translation initiation codon, To determine if editing may occur in a chimeric mRNA, the N-terminal part of psbL containing the editing site was translationally fused with the aadA and kan bacte rial genes. The chimeric constructs were introduced into the tobacco p lastid genome by targeted gene insertion, Editing of the chimeric mRNA s indicated that the 98 nt fragment spanning the psbL editing site con tains all cis information required for editing, Expression of the chim eric gene transcripts led to a significant decrease in the editing eff iciency of the endogenous psbL mRNA, However, the efficiency of editin g in the transplastomic lines was unchanged for four sites in the rpoB and ndhB mRNAs, Reduced efficiency of psbL editing, but not of the ot her four sites, in the transplastomic lines indicates depletion of psb L-specific editing factor(s), This finding implicates the involvement of site-specific factors in editing of plastid mRNAs in higher plants.