Terminator (genetics)

These processes include the direct interaction of the mRNA secondary structure with the complex and/or the indirect activities of recruited termination factors.

The mechanism of termination is hypothesized to occur through a combination of direct promotion of dissociation through allosteric effects of hairpin binding interactions with the RNA polymerase and "competitive kinetics".

[5][6] Additionally, the elongation protein factor NusA interacts with the RNA polymerase and the hairpin structure to stimulate transcriptional termination.

This is a modified guanine added to the front of mRNA, which prevents the exonuclease from binding and degrading the RNA strand.

The allosteric model suggests that termination occurs due to the structural change of the RNA polymerase unit after binding to or losing some of its associated proteins, making it detach from the DNA strand after the signal.

However, upon transcribing over the poly-A signals on the DNA template, a conformational shift is induced in the RNA polymerase from the proposed loss of associated proteins from its carboxyl terminal domain.

This change of conformation reduces RNA polymerase's processivity making the enzyme more prone to dissociating from its DNA-RNA substrate.

[12] Finally, Pol II also have poly(A)-independent modes of termination, which is required when it transcribes snRNA and snoRNA genes in yeast.

[9] Some human mechanism, possibly PCF11, seems to cause premature termination when pol II transcribes HIV genes.

Simplified schematics of the mechanisms of prokaryotic transcriptional termination. In Rho-independent termination, a terminating hairpin forms on the nascent mRNA interacting with the NusA protein to stimulate release of the transcript from the RNA polymerase complex (top). In Rho-dependent termination, the Rho protein binds at the upstream rut site, translocates down the mRNA, and interacts with the RNA polymerase complex to stimulate release of the transcript.