QUANTIFYING TERMINATION OF TRANSCRIPTION BY SPINACH CHLOROPLAST RNA-POLYMERASE USING SUPERCOILED TEMPLATES CONTAINING TANDEM COPIES OF THE THRA TERMINATOR

A method was developed to quantify the efficiency with which a transcription terminator of the E. coli threonine attenuator, thra, is recognized by spinach chloroplast RNA polymerase. Multiple tandem copies of the thra terminator were cloned downstream from a strong chloroplast promoter. These supercoiled DNAs were transcribed in vitro and the termination efficiency determined by quantifying the relative amount of transcripts that ended at each successive terminator. A simple calculation showed that about 63% of the RNAs made by spinach chloroplast or T7 RNA polymerase were terminated at each thra terminator.