The origin recognition complex (ORC) is a highly conserved complex found in all eukaryotes.  It is composed of six proteins with a mass of 400 kD.  ORC binds to the yeast A and B1 elements on the A-T–rich strand and is associated with ARS elements throughout the cell cycle.

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#Unit 3. Fundamental Processes

Point mutations that reduce termination efficiency usually occur within the stem region of the hairpin, replacing GC base pairs with weaker AT base pairs, or in the U-rich sequence, supporting the importance of these sequences in the mechanism of termination.

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#Unit 3. Fundamental Processes

Readthrough transcripts refer to the fraction of transcripts that are not stopped by the terminator. (Readthrough is the same term used in translation to describe a ribosome’s suppression of termination codons.) 

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#Unit 3. Fundamental Processes

the termination event can be prevented by specific ancillary factors that interact with RNA and/or RNA polymerase, a situation referred to as antitermination.

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#Unit 3. Fundamental Processes

There are other parallels between initiation and termination. Both require breaking of hydrogen bonds (initial melting of DNA at initiation and RNA–DNA dissociation at termination), and both can utilize additional proteins (sigma factors, activators, repressors, and rho factor) that interact with the core enzyme.

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#Unit 3. Fundamental Processes

Initiation relies solely upon the interaction between RNA polymerase and duplex DNA, however, the termination event also involves recognition of signals in the transcript by RNA polymerase.

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#Unit 3. Fundamental Processes

Rho factor is an essential protein in E. coli that causes transcription termination.