Analysis of the promoter region of the RuBisCO gene of Arthrospira (Spirulina) platensis

Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO), a key enzyme involved with photosynthetic carbon assimilation, catalyzes the carboxylation and oxidization of ribulose-1,5-bisphosphate. Interestingly, the promoter region of this gene from Arthrospira platensis could drive the expression of a downstream gene in Escherichia coli. In this study, using green fluorescent protein as a reporter of gene expression, the structure and function of the promoter region of the RuBisCO gene of A. platensis was analyzed. There are three hypothetical promoter elements predicted in the 200 bp upstream of the open reading frame (ORF) of RuBisCO. Through deletion analysis of the promoter, it was demonstrated that one of these elements was the active promoter, which was located between ?94 and the ORF of RuBisCO. The ?35 box of the RuBisCO promoter (TTGACT) was very similar to that of the rpoD gene (TTGACA) of E. coli, with only the sixth nucleotide divergent. Site-directed mutational analysis showed that when the sixth nucleotide (T) was changed to A, the activity of the promoter remained unchanged. However, when the first and second Ts were mutated, the activities of the promoters decreased drastically. Determining the structure and function of promoters would help elucidate the molecular mechanisms of the gene expression and regulation.