Figure 1.

(A) Effects of the Kozak stem (KS) element inserted into the center of the CaMV leader on shunt- (line 4 vs. 1) and scanning-dependent (line 3 vs. 2) expression in plant protoplasts as well as on infectivity of the corresponding CaMV mutants in turnip plants. Several sORFs in the leader are shown by boxes, point mutations of the sORFs A, B, and C indicated by crosses. Relative CAT expression levels in the presence or the absence of TAV are given. (B) Deletions and insertions generated in planta on passage of the CaMV mutant containing the 38-nt KS sequence (in lowercase) between positions 222 and 239 of the 35S RNA leader. Direct repeats at the borders of four deletions are shown by arrows. Insertions in the two deletion sites are indicated by triangles. (C) An example of restoration of stem section 3 in the CaMV leader structure because of the deletions/insertions. The extended hairpin structure of the wild-type leader comprising three stem sections and the bowl region with the putative RNA encapsidation signal is depicted schematically. The ribosome shunt pathway bypassing the hairpin is indicated by a curved arrow; the shunt-mediating sORF A is shown by a box. Close ups of the stem section 3 region of wild-type, mutant, and revertant leaders are shown. Nucleotides differing from the wild-type sequence are in lowercase. Numbering is from the 5′ end of 35S RNA (new numbering for the deletion/insertion variants is in italics).