Xylanase gene from Streptomyces sp. PC22 was cloned by using two host-vector systems which were Streptomyces lividans TK21 and pIJ699 or pIJ702 and E.coli DH5alpha and pUC18. With Streptomyces lividans TK21 as a host a host a stable clone, namely S-21 was obtained with pIJ699 as a cloning vector. Clone S-21 had xylanase activity of 1.21 U.ml-1 which was about 2 folds higher than that of the host. However, no plasmid was detected from this clone. With pIJ702 as a cloning vector, one clone showing clear zone on a selective xylan containing agar plate was obtained but it lost the xylanase activity upon cultivation in liquid medium. Futhermore, the plasmid from this clone showed similarity in size to pIJ702. The above results indicated that xylanase gene from Streptomyces sp. PC22 may be homologous to that of Streptomyces lividans TK21 causing recombination and integration or recombination and deletion as in the cases of pIJ699 and pIJ702 as cloning vectors, respectively. With E.coli DH5alpha as a host, a clone, namely E-8, showing narrow clear zone on a selective plate after exposing to chloroform was obtained. It had xylanase activity of 0.25 U.mg-1 of protein which was about 3 folds higher than of the host. Clone E-8 possessed a recombinant plasmid of about 4.6 kb which contained DNA insert of about 1.9 kb.
