The locations of numerous lacI− and lacIS mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI− mutations were found to occur in the 5'-upstream region of the gene, while lacIS mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene? The locations of numerous and mutations have been determined within the DNA sequence of the gene. Among these, mutations were found to occur in the 5'-upstream region of the gene, while mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the gene? The mutations described are consistent with the structure of the lac repressor. The mutations described are not consistent with the structure of the lac repressor.