Abstract
Squalene synthase (SS) synthesizes the first lipophilic precursor squalene in phytosterol synthesis pathway (Suzuki et al 2002, Akamine et al 2003, Lee et al 2004, Uchida et al 2009). In a microalga Botryococcus braunii, methylsqualenes and their derivatives are released to extracellular matrix as secondary metabolites. The cDNAs clone of B. braunii SS gene (BbSS) was isolated and functionally characterized (Okada et al 2000). Prominent SS enzyme activity was detected transiently immediately after inoculation into a fresh medium, and weaker activity was observed continuously in the other culture periods. In order to analyze gene expression of BbSS, we have isolated corresponding genomic clones through PCR amplification and cloning to obtain the 0.55-kb and 1.4-kb clones. Nucleotide sequencing of these two clones revealed existence of 223-bp and 756-bp introns after 2nd base of 52nd amino-acid residue and 3rd base of 232nd amino-acid residue, respectively. We are further isolating other genomic clones spanning in the entire regions of the gene, including the 5' upstream region.
