Unusual promoter-independent transcription reactions with bacteriophage RNA polymerases

Efficient transcription reactions of DNA-dependent RNA polymerases require the presence of a specific promoter sequence. This report shows that in the absence of their cognate promoter, two bacteriophage RNA polymerases are capable of performing unusual transcription reactions: (i) the DNA template serves also as a primer for RNA synthesis and this leads to hybrid DNA/RNA molecules, (ii) if the DNA template forms a hairpin structure, the linear DNA can be transcribed via the 'rolling circle' mechanism.