The Construction Of Recombinant Saccharomyces Cerevisiae Producing β-carotene And Study Of Metabolic Pathway

We captured three genes,crtE,encoding the geranylgeranyl pyrophosphate synthase,crtl,encoding the carotene desaturase,crtYB,encoding the phytoene synthase/lycopene p-cyclase,from the strain Xanthophyllomyces dendrorhous ATCC24202 by the reverse transcriptase PCR.We then introduced the β-carotene biosynthesis pathway,i.e.integrating above three genes at the delta locus in Saccharomyces cerevisiae BY4742 that can synthesize the precursor farnesyl pyrophosphate by the DNA assembler method.The resultant HCCB08531 produced β-carotene up to 3.68 mg/g(dry weight).We employed three strategies,enhancing the precursor FPP synthesis,down-regulating the ERG9 gene and over-expressing several genes encoding key enzymes to study the metabolic pathway of HCCB08531 with the expectation to improve the production of β-carotene.However,no improvement was found for β-carotene production although we did observe much accumulation of an intermediate lycopene when the native promoter of ERG9 was replaced with the MET3 promoter in the HCCB08531 and obvious decrease of the intermediate lycopene in the HCCB08531FPP and HCCB08531pYKT-tHMGl.We speculate that the accumulation of much precursor represses activities of some key enzymes,which results in no improvement forβ-carotene production.