CHARACTERIZATION OF AN UNUSUAL, SEQUENCE-SPECIFIC TERMINATION SIGNAL FOR T7 RNA-POLYMERASE

We have characterized an unusual type of termination signal for T7 RNA polymerase that requires a conserved 7-base pair sequence in the DNA (ATCTGTT in the nontemplate strand). Each of the nucleotides within th is sequence is critical for function, as any substitutions abolish ter mination. The primary site of termination occurs 7 nucleotides downstr eam from this sequence but is context-independent (that is, the sequen ce around the site of termination, and in particular the nucleotide at the site of termination, need not be conserved). Termination requires the presence of the conserved sequence and its complement in duplex D NA and is abolished or diminished if the signal is placed downstream o f regions in which the non-template strand is missing or mismatched. U nder the latter conditions, much of the RNA product remains associated with the template. The latter results suggest that proper resolution of the transcription bubble at its trailing edge and/or displacement o f the RNA product are required for termination at this class of signal .