Functional transcription elongation complexes from synthetic RNA-DNA bubble duplexes.

A synthetic RNA-DNA bubble duplex construct intended to mimic the nucleic acid framework of a functional transcription elongation complex was designed and assembled. The construct consisted of a double-stranded DNA duplex of variable length (the template and nontemplate strands) containing an internal noncomplementary DNA "bubble" sequence. The 3' end of an RNA oligonucleotide that is partially complementary to the template DNA strand was hybridized within the DNA bubble to form an RNA-DNA duplex with a non-complementary 5'-terminal RNA tail. The addition of either Escherichia coli or T7 RNA polymerase to this construct formed a complex that synthesized RNA with good efficiency from the hybridized RNA primer in a template-directed and processive manner, and displayed other features of a normal promoter-initiated transcription elongation complex. Other such constructs can be designed to examine many of the functional and regulatory properties of transcription systems.