Question

Transcriptional regulation is important for organisms to respond to their environment. Some of the features of regulation act in cis and some act in trans. Please describe what is meant by each of these terms and then give an example of each from prokaryotes and give an example of each from eukaryotes.

Answer 1

Transcriptional regulation
In molecular biology and genetics, transcriptional regulation is the means by which a cell regulates the conversion of DNA to RNA, thereby orchestrating gene activity.
Cis-regulatory elements (CREs) are regions of non-coding DNA which regulate the transcription of neighboring genes. CREs are vital components of genetic regulatory networks, which in turn control morphogenesis, the development of anatomy, and other aspects of embryonic development, studied in evolutionary developmental biology.CREs are found in the vicinity of the genes that they regulate. CREs typically regulate gene transcription by binding to transcription factors. A single transcription factor may bind to many CREs, and hence control the expression of many genes
An example of a cis-acting regulatory sequence is the operator in the lac operon. This DNA sequence is bound by the lac repressor, which, in turn, prevents transcription of the adjacent genes on the same DNA molecule. The lac operator is, thus, considered to "act in cis" on the regulation of the nearby genes. The operator itself does not code for any protein or RNA.
Trans-acting (trans-regulatory, trans-regulation), in general, means "acting from a different molecule" (i.e., intermolecular). It may be considered the opposite of cis-acting (cis-regulatory, cis-regulation), which, in general, means "acting from the same molecule" (i.e., intramolecular). In the context of transcription regulation, a trans-acting factor is usually a regulatory protein that binds to DNA.[1] The binding of a trans-acting factor to a cis-regulatory element in DNA can cause changes in transcriptional expression levels. microRNAs or other diffusible molecules are also examples of trans-acting factors that can regulate target sequences.[2] The trans-acting gene may be on a different chromosome to the target gene, but the activity is via the intermediary protein or RNA that it encodes. Cis-acting elements, on the other hand, do not code for protein or RNA. Both the trans-acting gene and the protein/RNA that it encodes are said to "act in trans" on the target gene.
Examples of trans-acting factors include the genes for:[2] Subunits of RNA polymerase Proteins that bind to RNA polymerase to stabilize the initiation complex Proteins that bind to all promoters of specific sequences, but not to RNA polymerase (TFIID factors) Proteins that bind to a few promoters and are required for transcription initiation (positive regulators of gene expression)