Deletion of DNA sequences flanking an Mr 19,000 zein gene reduces its transcriptional activity in heterologous plant tissues.

Analysis of a series of clones containing deletions in the 5' noncoding sequence of a gene encoding an Mr 19,000 zein allowed identification of a region required for maximal transcription. Transcriptional activity was assayed in two heterologous plant systems. In one system, the Ti plasmid was used to introduce the modified zein genes into the sunflower genome. In the other system, electroporation was used to transform carrot protoplasts with plasmids containing the zein genes. For the electroporation experiments, the 5' noncoding sequences from the zein clones were linked to the protein coding sequence of chloramphenicol acetyl transferase. The results showed that an upstream sequence, delimited by nucleotides -337 and -125 with respect to the mRNA cap site, is required for maximal transcription of the gene. In contrast, very low levels of transcription were directed by constructs that contained 125 bp of 5' noncoding sequence that included the CAAT and TATA boxes, suggesting that the additional sequences (-337 to -125) further 5' exert a quantitative effect on transcription. Examination of the additional 5' sequences showed five regions that share homology with the SV40 enhancer core sequence.