With the use of photoresponsive T7 promoters tethering two 2¢-methylazo-benzenes or 2¢,6¢-dimethylazobenzenes, highly efficient photoregulation of DNA transcription was obtained. After UV-A light irradiation (320–400 nm), the rate of transcription with T7 RNA polymerase and a photoresponsive promoter involving two 2¢,6¢-dimethylazobenzenes was 10-fold faster than that after visible light irradiation (400–600 nm).