세균인 Paenibacillus sp. DG-22의 유전체 DNA library가 제조되었으며, ${eta}-xylosidase-$양성 클론이 형광기질인 $4-methylumbelliferyl-{eta}-D-xylopyranoside$ $({eta}MUX)$를 사용하여 확인되었다. 이 클론으로부터 재조합 플라스미드가 분리되었고 삽입된 4.3-kb 크기 DNA의 염기서열이 결정되었다. ${beta}-xylosidase$ 유전자는 분자량이 78.710 dal-ton이고 pI가 5.0인 701개의 아미노산을 암호화하는 2,106 염기쌍의 열린해독틀(ORF)로 구성되어있었다. xylA 유전자산물의 추론된 아미노산 서열은 과(family) 52에 속하는 클리코실 가수분해효소로 분류된 ${beta}-xylosidase$들과 상당한 유사성을 가지고 있었다. 이 xylA 유전자에 6개의 히스티딘-꼬리표를 붙이기 위해 pQE60 발현벡터에 다시 클로닝하였다. 재조합 ${beta}-xylosidase$ $(XylA-H_6)$가 열처리와 고정화금속친화성 크로마토그래피(IMAC)에 의해 순수하게 정제되었다. $XylA-H_6$ 효소의 최적 pH와 온도는 각각 pH 5.5-6.0과 $60^{circ}C$이었다.
A genomic DNA library of the bacterium Paenibacillus sp. DG-22 was constructed and the ${eta}-xylosi-dase-positive$ clones were identified using the fluorogenic substrate $4-methylumbelliferyl-{eta}-D-xylopyr-anoside$ $({eta}MUX)$. A recombinant plasmid was isolated from the clone and 4.3-kb inserted DNA was sequenced. The ${eta}-xylosidase$ gene (xylA) was comprised of a 2,106 bp open reading frame (ORF) en-coding 701 amino acids with a molecular weight of 78,710 dalton and a pI of 5.0. The deduced amino acid sequence of the xylA gene product had significant similarity with ${eta}-xylosidases$ classified into family 52 of glycosyl hydrolases. The xylA gene was subcloned into the pQE60 expression vector to fuse with six histidine-tag. The recombinant ${eta}-xylosidase$ $(XylA-H_6)$ was purified to homogeneity by heat-treatment and immobilized metal affinity chromatography. The pH and temperature optima of the $XylA-H_6$ enzyme were pH 5.5-6.0 and $60^{circ}C$, respectively.
