With this enzyme, homogeneously labeled single-stranded RNA can be generated. Transcripts can be nonradioactively labeled with biotin or DIG-11-UTP or radioactively labeled to high specific activity with [α-32P]- or [α-35S]-labeled nucleotides. T3 RNA polymerase is a DNA-dependent RNA polymerase that is highly specific for its promoter. Only DNA downstream from the T3 promoter will be transcribed.