ABSTRACT
XYL1 gene,which encodes xylose reductase with dual coenzyme activity from Candida tropicalis,was transformed into Pichia pastoris X-33 by expression vector pGAPZB.The recombination strain was immobilized in Ca-alginate beads and fermentation characterization is studied using corn cob hydrolysates.Fermentation conditions were as follow:initial pH value 6.0,30℃,initial cell concentration of 20%,the Liquid volume of 28%,rotation speed 130r/min.The average xylitol yield was 37.5% on the optimum condition.This result is expected to provide a new alternative method for producing xylitol on a large scale by bioconversion.
ABSTRACT
The purpose of this review is to confirm the reason resulted the gene silence and explore the countermeasure avoiding the gene silence in transgene plant. The method is to divide the gene silencing into transcriptional gene silencing(TGS) and posttranscriptional gene silencing(PTGS). Several models resulted PTGS were analyzed by RNA threshold model, ectopic pairing and aberrant RNA model and ds-RNA model. The results showed that it was important to decide the phenomena of restraining transgene silencing and the mechanism of PTGS. The strategies of identification of gene function and prevention of virus were presented by RNAi and gene silencing respectively, etc.