Figure 1.

Comparison of short (Upper) and long (Lower) RNA⋅DNA hybrid models of transcription complex. The stabilization of RNA (red) in the ternary transcription results from protein–RNA contacts (Upper) or is caused primarily by the establishment of full-length RNA⋅DNA hybrids (Lower). The crystal structure of transcribing T7 RNAP (12) looks like the schematic structure (Upper Left). Temiakov et al. (15) present data that the elongating T7 RNAP–transcription complex looks like the structure presented (Bottom Center) and, thus, is similar to the Escherichia coli RNAP (7). It is suggested that the structure (Upper Center) may correspond to transcription complex engaged in unproductive reiterative slippage synthesis.