Translocation of Escherichia coli RNA polymerase against a protein roadblock in vivo highlights a passive sliding mechanism for transcript elongation.

摘要: Current models for transcription elongation infer that RNA polymerase (RNAP) moves along the template by a passive sliding mechanism takes advantage of random lateral oscillations in which single basepair movements interconvert complex between pre- and post-translocated states. Such translocational equilibrium was tested vivo systematic change templated NTP is to be incorporated RNAP, temporarily roadblocked lac repressor. Our results show that, under these conditions hinder forward movement polymerase, able extend its chain one nucleotide further when incoming kinetically favoured substrate (i.e. low K(m)). The addition an extra destabilizes repressor-operator roadblock leading increase transcriptional readthrough. Similar are obtained NTPs less substrates high K(m)s) specifically increasing their intracellular concentrations. Altogether, data consistent with model RNAP translocation binding. They also suggest fluctuations pools may play key role gene regulation at transcript level.