Structural feature of sorghum chloroplast psbA gene and regulation effects of its 5'-noncoding region*

Comparative analysis reveals remarkable homology between the sequences of both psbA gene nucleotidesand the inferred amino acids of sorghum, a C4 plant, and those of rice, a C3 plant. The 5'-noncoding region of sorghum psbA gene contains the conservative promoter elements, " - 35" element and " - 10" element, like the prokaryote and the promoter element, TATA box, like the eukaryote. As compared with that of the rice, an extra sequence of 7 bp is found in the leader sequence of the mRNA in the former. Using an in vitro system, it has been demonstrated that protein factor exists in sorghum chloroplast protein extract which specifically binds to the 5'-noncoding region of psbA gene. Measurement of the expression of luciferase shows a 2-5 time greater reaction of the expression plasmids pALqs which contain leader region of sorghum psbA gene than that of the expression plasmids pALqr which contain leader region of rice psbA gene in E. coli.