Restoration of site V editing in the single-nucleotide-deletion mutant (construct pRB67-Δ1) by introduction of a compensatory point mutation, creating an editable C the correct distance from the upstream cis-element (construct pRB73-Δ1/cm). (A) Sequence analysis to test for transgene mRNA editing in the Nt-pRB73-Δ1/cm transplastomic lines. For comparison, editing in the Nt-pRB67-Δ1 lines also is shown. PCR and sequencing primers are as in Fig. 3. Arrowheads point to the editing positions in the cDNA lanes (G in DNA; A in cDNA), a dash indicates lack of editing, and roman numerals mark editing site IV. Note the lack of editing at site V in Nt-pRB67-Δ1 (dash) and restoration of editing after conversion of the downstream nucleotide into a cytidine in Nt-pRB73-Δ1/cm (arrowhead). (B) Restoration of editing in the Nt-pRB73-Δ1/cm transplastomic lines. The single-nucleotide deletion in the spacer, abolishing editing at site V in Nt-pRB67-Δ1 (solid arrow in the wild-type sequence; open arrow in the pRB73-Δ1/cm sequence), is compensated by mutational creation of an “in-phase” cytidine immediately 3′ of editing site V (stippled arrow).