Before revision:  Recent {\it in-vivo} experiments with single cells have established that transcription takes place in ``bursts'' or ``pulses'' . In this letter we present a model that captures not only the mechano-chemistry of individual RNAPs and their steric interactions but also the switching of the gene between the ON and OFF states.
After revision:  Recent {\it in-vivo} experiments with single cells have established that transcription takes place in "bursts" or "pulses" . In this letter we present a model that captures not only the mechano-chemistry of individual RNAPs and their steric interactions but also the switching of the gene between the ON and OFF states.