A gene consists of a transcriptional region and a regulatory region. The transcriptional region is the part of DNA to be transcribed
into a primary transcript (an RNA molecule complementary to the transcriptional region). The regulatory region can be divided into cis-regulatory (or cis-acting) elements
and trans-regulatory (or trans-acting) elements. The cis-regulatory elements are the binding sites of transcription factors which are the proteins that,
upon binding with cis-regulatory elements, can affect (either enhance or repress) transcription. The trans-regulatory elements are the DNA sequences that encode transcription factors.
The cis-acting elements may be divided into the following four types:
The DNA element where the transcription initiation takes place.
The element that, upon binding with transcription factors, can enhance transcription. The transcription factors that bind to enhancers are called transcriptional activators.
The element that, upon binding with transcription factors, can repress transcription. The transcription factors that bind to silencers are called repressors.
The recognition site of certain transcription factors.
Figure 4-C-1. Gene organization. The
transcription region consists of exons and introns. The regulatory
elements include promoter, response element, enhancer and silencer (not
shown). Downstream refers to the direction of transcription
and upstream is opposite to the transcription direction. The numbering
of base pairs in the promoter region is as follows.
The number increases along the direction of transcription, with "+1" assigned for the
initiation site. There is no "0" position. The base pair just upstream of +1 is numbered "-1", not