RESUMEN
XylA gene of Streptomyces violaceoniger [Drocourt et coll. 1988] code for a D-xlyose isomerase activity which is used as a D-glucose isomerase activity in large scale. This gene is a part of regulated region involved in xylose utilization [Marcel et coll. 1987]. Sequence determination of this region enabled us to characterize xylB gene [Xylulose kinase activity] and xylX gene which is involved in xylA and xylB expression. In order to construct a new strain having a strong and constitutive glucose isomerase activity, a newly isolated strong streptomyces promoter [P1 promoter], has been cloned behind xylA gene. To avoid instability of plasmid and glucose-isomerase activity, the Pl-xylA gene of S. violaceoniger has been integrated into the chromosome, using the integrative vector pTS55. The resultant CBS1 strain has four to five fold higher glucose-isomerase activity in absence of xylose compared to that of strain SV1 fully induced by xylose. In addition, specific glucose-isomerase activity of CBS1 strain increases in the secondary growth phase, in contrast to wild type and SV1 strains