Transcription termination comes in two forms in "E. coli" cells. Rho-dependent termination requires the binding of a termination protein called Rho factor to the transcriptional machinery at the terminator region, whereas Rho-independent termination is achieved by conformational changes in the transcript itself. This article presents a test experiment that was designed to study the mechanism of action of the Rho protein. Artificial substrates to analyze Rho action were constructed and tested in cell-free reactions. A recombinant plasmid was prepared by inserting a short sequence into the plasmid DNA. (Contains 1 figure and 1 footnote.)