A new method for gene synthesis and its high-level expression.

An optimized Citrobacter braakii phytase gene, appA-c, was chemically synthesized by oligonucleotides synthesis and over-lap PCR method. The appA-c gene encoding 423 amino acids was cloned into expression vector pPIC9 and transformed into methylotropic yeast Pichia pastoris. From about 2000 transformants, 400 transformants exhibiting phytase activity were obtained.