In order to investigate the regulatory mechanisms of the expression of inducible repair genes, we focused on the specific nucleotide sequences in the promoter regions responsible for their inducibility. First of all, plasmid pCH10 and pS206, which contain Pada-lacZ or PalkA-lacZ fused gene, respectively, were made. In these plasmids the structural lacZ gene is expressed under the control of ada or alkA promoter in fused genes. It is very easy and convenient to assay the promoting activities of the promoters owing to the simple assay technique for the β-galactosidase activities from lacZ gene. In the present study the identification of the regulatory region for gene induction was carried out using Bal 31 nuclease digestion only for the alkA gene. The promoter regions of the PalkA-lacZ fused gene was shortened from 5’-end with Bal₃I digestion and recloned into the pBR322 plasmid after adding EcoRI linker DNA. We isolated the clones containing the recombinant hybrid plasmids in which the expression of the fused genes were detected or not. The length of promoters in the plasmids isolated were determined and the critical region was deduced by comparing with the nucleotide sequences of the original alkA gene promoter. At present it is found that the site for the regulation of alkA gene is located is the promoter region between -130 and -40 bases upstream from the alkA gene start codon. pJC9 plasmid which contains additional 140 base pairs (bp) upstream from the start site of the alkA structural region shows the β-galactosidase activities, but the pJC57 which contains additional 40 bp upstream ahead of the alkA gene does not. We are planning to construct the plasmids which were introduced further deletion into the remaining region of pJC9 plasmid from 5’-end of the promoter region. In addition the inducibilities of lacZ 9gene expression by the recombinant promoters will be compared to the sequence of the remaining promoter sequences.