SEGMENTS ENCODING 5'-UNTRANSLATED LEADERS OF GENES FOR THYLAKOID PROTEINS CONTAIN CIS-ELEMENTS ESSENTIAL FOR TRANSCRIPTION

The promoter region -118/-29 of the spinach PetH gene encoding the fer redoxin-NADP(+)-oxidoreductase contains crucial cis-elements for the r egulated expression, while sequences for the 5'-untranslated leader de termine the quantitative expression of chimeric GUS gene fusions in tr ansgenic tobacco. Deletion of leader sequences in chimeric GUS gene fu sions of the spinach PetE and PsaF genes (for plastocyanin and the sub unit III of photosystem I, respectively) results also in a decline in the GUS activity. Appropriate gene constructs and run-on transcription assays demonstrate unambiguously that the leaders of all three genes are involved in transcription rather than in post-transcriptional proc esses. They appear to contain gene-specific control elements rather th an cis-determinants for general initiation factors. Expression-relevan t segments in the PsaF and PetH leaders contain two CT-rich sequences, designated CT-LB and CT-B, of which at least the former binds to a pr otein factor in gel mobility shift assays. These motifs are not found in the PetE leader. The findings imply that leader sequences may conta in cis-elements that are essential for the transcription, that they in fluence GUS gene expression quantitatively rather than qualitatively, and that these elements, as those of promoters, can be quite variable in sequence.