오페론(Operon)에 대한 발표자료 (영어)

Regulation of gene expression
Transcription often is controlled at the stage of initiation. Transcription is not usually controlled at elongation, but may be controlled at termination to determine whether RNA polymerase is allowed to proceed past a terminator to the gene(s) beyond.
In eukaryotic cells, processing of the RNA product may be regulated at the stages of modification, splicing, transport, or stability. In bacteria, an mRNA is in principle available for translation as soon as (or even while) it is being synthesized, and these stages of control are not available.
Translation may be regulated, usually at the stages of initiation and termination (like transcription). Regulation of initiation is formally analogous to the regulation of transcription: the circuitry can be drawn in similar terms for regulating initiation of transcription on DNA or initiation of translation on RNA. (*miRNA, and siRNA)
Terminology
A trans-acting product can function on any copy of its target DNA. This implies that it is a diffusible protein or RNA.
A cis-acting site affects the activity only of sequences on its own molecule of DNA (or RNA); this property usually implies




Repressor can make a loop in DNA
Caption:
If both dimers in a repressor tetramer bind to DNA, the DNA between the two binding sites is held in a loop.
It was originally thought that repressor binding would occlude RNA polymerase from binding to the promoter. However, we now know that the two proteins may be bound to DNA simultaneously, and the binding of repressor actually enhances the binding of RNA polymerase! But the bound enzyme is prevented from initiating transcription.
Binding of repressor at the operator stimulates binding of RNA polymerase at the promoter.
When a repressor tetramer binds to two operators, the stretch of DNA between them is forced into a tight loop. (The blue structure in the center of the looped DNA represents CAP, another regulator protein that binds in this region.)