Identification and Characterization of the Point Mutation Which Affects the Transcription Level of the Chromosomal 3-N-Acetyltransferase Gene of Streptomyces griseus SS-1198

We determined the molecular basis for the enhanced expression of the aac(3)-Xa gene encoding an aminoglycoside 3-N-acetyltransferase in Streptomyces griseus. A C→T substitution was identified at the putative promoter of the mutant gene. RNA analyses demonstrated that the substitution caused a marked increase in the production of the gene-specific transcripts. Therefore, it seemed very likely that the aac(3)-Xa gene was activated by the substitution resulting in the emergence of a stronger promoter.