ABSTRACT
The purpose of this investigation is to improve ethanol production and decrease acetate formation in Saccharomyces cerevisiae strain YS2-?adh2.The strain YS2-?adh2 with deleted alcohol dehydrogenase Ⅱ(adh2) gene was isolated in our lab with higher ethanol production than that of the strain YS2.The ace-taldehyde dehydrogenase Ⅵ(ald6) gene encoded a cytosolic acetaldehyde dehydrogenase,a key enzyme of the pyruvate dehydrogenase(PDH) bypass,transfers acetaldehyde to acetate.To disrupt ald6 gene of the strain YS2-?adh2,ald6 gene targeting cassettes were synthesized by long flanking homology PCR(LFH-PCR) and then were transformed into YS2-?adh2 mutants by LiAc/SS Carrier DNA/PEG method.Positive transformants were selected with G418 and further confirmed by PCR.Once correctly integrated into the genome,the selective marker was rescued by transforming the plasmid pSH65 into the positive transformants and inducing the Cre expression with a Cre/loxP-mediated marker removal procedure.We named the ald6 gene knocked-out strain as YS2-?adh2-?ald6 which has a 12.5% higher ethanol production and a 18% lower acetate formation compared to the strain YS2.
ABSTRACT
Acyl carrier protein is an essential component involved in the biosynthesis of DHA(Docosahexaenoic Acid) via PKS(Polyketide synthase) pathway,which takes the growing acyl chain from one enzyme to another.One cDNA clone,with high homology of ACP,was isolated from Schizochytrium sp.FJU-512 cDNA library.The deduced amino acid sequence contained 142 residues with isoelectric point of 5.04 and had the 4'-phosphopantetheine prosthetic(4'-PP) binding site.The target fragment was digested with BamHⅠ/HindⅢand inserted into the expression vector pET-30a resulting in the plasmid pET-30a/acp.The recombinant vector was transformed into E.coli BL21(DE3) and induced by IPTG.SDS-PAGE analysis demonstrated that ACP was effectively expressed.
ABSTRACT
To improve ethanol production in Saccharomyces cerevisiae,an integration plasmid pUPGKAT with PGK promoter(phosphoglycerate kinase promoter),adh1 gene(the coding sequences of alcohol dehydrogenaseⅠ) and CYC1 terminator(Cytochrome c transcription terminator) was constructed.Firstly,a fusion fragment composed of PGK promoter and adh1 gene was generated by over lap extension PCR and ligated into pUG6 resulting in plasmid pUPGKA.Subsequently,CYC1 termi nator was amplified from pSH65 by PCR and ligated to the SpeⅠand SacⅡrestriction site of pUPGKA.To integrate PGK-adh1-CYC1 into S.cerevisiae genome,pUPGKAT was digested by TthⅢⅠand the lin-earized plasmid was used to transform S.cerevisiae YS2-△adh2(adh2 disrupted strain) by lithium acetate method.The yeast mutant YS2-△adh2-adh1 which had the adh1 gene placed under the PGK promoter and harbored the adh2 deletion was constructed.Anaerobic fermentation showed overexpression of adh1 by PGK promoter resulted in a 8.84% higher ethanol production compared to YS2-△adh2.
ABSTRACT
1.6 kb ?4-desaturase gene(FAD4)was amplified by PCR using plasmid pGEM-TFAD4 as template.The fragment was subcloned into the HindⅢ/XbaⅠrestriction site of pYES2.0 vector.Recombinant plasmid pYFAD4 was transformed into Saccharomyces cerevisiae strain INVScl for expression.It was found to exhibit ?4-fatty acid desaturase activity in the recombinant S.cerevisiae YFAD4 in the presence of exogenous fatty acid substrate docosapentaenoic acid(100?mol/L)under introduction of GAL1.Expression of the FAD4 under appropriate media and temperature conditions led to the production of DHA and it reached 41.13% of the total yeast fatty acid by GC detection.It was suggested that the protein encoded by FAD4 could specifically catalyze DPA into DHA.
ABSTRACT
The sfa1 gene encoded a bifunctional enzyme with the activities of both alcohol dehydrogenase and glutathione-dependent formaldehyde dehydrogenase in Saccharomyces cerevisiae.The gene disruption cassette produced by PCR using the same long oligonucleotides which comprise 19 or 22 nucleotides complementary to sequences in the templates(pUG6 and pUG66 marker plasmid)at 3' end and 45 nucleotides at 5' end that annealed to sites upstream or downstream of the genomic target sequence to be deleted.After two linear disruption cassettes with a Cre/loxP mediated marker were transformed into the cells of Saccharomyces cerevisiae YS-1,the positive transformants were checked by PCR to correct the integration of the cassette and concurrent deletion of the chromosomal target sequence.Once correctly integrated into the genome,the select marker can be efficiently rescued by transformating the plasmid pSH47 into YS-1 and inducing the Cre expression with a Cre/loxP-mediated marker removal procedure.The expression of the Cre recombinase finally resulted in the removal of the marker gene,leaving behind a single loxP site at the chromosomal locus.The diploid mutant YS-1-sfa1 was generated,which could enhance the output of ethanol with 8.0% by shaking culture in flask compared with the original strain YS-1.