The expression of xysA, a gene encoding for an endoxylanase from Streptomyces halstedii JM8, is repressed by glucose. In order to define the regions involved in its regulation, several deletions were made in the 475 bp xysA promoter and were studied using the melC operon from S. glaucescens as a reporter. Four of the deleted versions obtained were seen to be derepressed when driving melC or its own xysA gene expression in Streptomyces lividans. Quantitative assays revealed that the activity of xylanase produced under the control of these four deleted promoters was higher than the original one in the presence of glucose. Three regions - RI, R16 and R21 - involved in glucose repression were defined in this analysis: RI is a palindromic sequence that is highly conserved among xylanase gene promoters from Actinomycetes (-213 GAAAxxTTTCxGAAA -197) and, R16 and R21 define two new seven-pair conserved motifs, respectively (-113 5'-CCTTCCC-3' -106 in R16 and -76 5'-CGAACGG-3' -69 in R21) located in the untranslated mRNA. Gel shift assays demonstrated the existence of proteins that bind specifically to these regions.