Abstract
In order to overexpress constitutively the Kluyveromyces marxianus exoinulinase gene (INUI) in Saccharomyces cerevisiae, four episomal expression systems employing GAPDH, ADHI, PGK and ENOI promoters were constructed as p YIGP aADHI -INU, pPGK-INU, and pENOI- INU plasmids respectively, When S cereviais transformants harboring each plasmid were batchwisely cultivated in the fermentor containing 5% glucose medium no significant differences in the cell growth are observed How- ever the experession level of exoinulinase and plasmid stability showed a strong dependency on the promoter employed. The expression levels of exoinulinase were about 1.70 unit/ml for GAPDH promoter 1.67 unit/ml for PGK promoter, 1.29 unit /ml for ADH1 promoter, and 0.80 unit/ml for ENOl promoter. The plasmid stabilites were maintaines above 80% in all experession systems. except the GAPDH promoter system of 55%, Based on the plas- mid stability and expression level of exoinulinase the ADHl and PGK promoter system were selected for the fed - batch culture to overproduce exoinulinase By the intermittent feeding of yeast extract and glucose, both promoter systems gave the cell concentration of about 30 g-dry cell weight/1 byt the maximal exoinulinase activity of 3.70 unit/ml and plasmid stability of 96% in the ADH1 promoter were higher than those (2.70 unit/ml, 80%) of PGK sys- tem Taking into account the plasmid stability and extended culture time the ADH1 promoter systems would be the most feasible expression systems for the constitutive overproduction of exoinulinase through high cell-density fed- batch cultures using non-selective rich medium.
Klyyveromyces marxianus exoinulinase를 Saccharomyces cerevisiae에서 구성적으로 과발현 생산하기 위해, 구성적 promoter인 GAPDH, ADH1, PGK 및 ENOI promoters 하류에 exoinulinase 유전자 (INUI)의 ORF를 in frame으로 연결한 각각의 plasmi에 YIGP, pADHI,-INU, pPGK-INU 및 pENO-INU 를 구축하였다. 이들 각 plasmid를함유한 형질전환주 4종을 포도당 농도 5% 배지에서 회분배양한 결과 균체증식은 promoter에 따라 큰 차이를 보이지 않았지만 exoinulinase 발현수준과 plasmid 안정성은 사용한 promoter 에 크게 좌우되었다. 즉 exoinulinase 발현수준은 GAPDH PGK ADH1 ENO1 promoter 각각 1.70, 1.67 1.29, 0.80 unit/ml 였으며 plasmid 안정성은 GAPDH promoter 계의 55%를 제외하고 모두 80%이상으로 높게 나타났다. 이상의 plasmid 안정성과 exoinulinae 발현수준을 고려하여 ADH1 및 PGK 발현계를 선정하여 유가배양하였다 Yeast extract와 포도당을 간헐적으로 공급한 유가배양 결과, 두 발현계에서 약 30 g-DCW/1의 균체농도를 얻었지만, ADHI promoter 계에서는 3.70 unit/ml 의 최대 exoinulinase 활성과 96%의 plasmid 안정성을 보여TRh 반면에 PGK promoter 계는 각각 2.70 unit/ml/와 80%를 나타내었다. 따라서 plasmid 안정성과 긴 배양시간을 고려할 때 비선택적 영양배지를 사용하는 고농도세포 유가배양에서 ADH1 promoter가 exoinulinase 의 구성적 과발현, 생산에 더 적합할 것으로 사료된다.
