Potential memory and hysteretic effects in transcription.

Kinetic results of RNA-chain elongation catalysed by wheat-germ RNA polymerase II are analysed according to the concept that DNA-dependent conformational transitions of the transcription complex intervene during transcription. A model is presented, involving participation of several forms of the transcription complex with different catalytic properties, generated by the sequence and/or conformation of the DNA template and/or the experimental conditions. The available experimental data suggest that these forms are interconvertible. Examples in which hysteretic transitions might occur are outlined, such as termination of transcription and transition from abortive to productive elongation in the first steps of RNA synthesis. The slow catalytic adaptation of the transcription complex to the template sequence might be a more general phenomenon for enzyme systems acting on polynucleotide templates, in view of the recent proposal that enzyme memory effects may also have some importance in DNA replication and messenger RNA (mRNA) translation.