Question

list two properties a coactivator needs to allow initiation of transcription of a typical eukaryote gene AND briefly explain why these properties are necessary.

Answer 1

A coactivator is a type of transcriptional coregulator that binds to an activator (a transcription factor) to increase the rate of transciption of a gene or set of genes.The activator contains a DNA binding domain that binds either to a DNA promoter site or a specific DNA regulatory sequence called an enhancer.Binding of the activator-coactivator complex increases the speed of transcription by recruiting general transcription mavhinery to the promoter,therefore increasing gene expression.The use of activators and coactivators allows for highly specific expression of certain genes depending on cell type and developmental stage.

Some coactivators also have Histone acetyltransferase(HAT) activity.HATs form large multiprotein complexes that weaken the association of histones to DNA by acetylating the N_terminal histone tail.This provides more space for the transcription machinery to bind to the promoter,therefore increasing gene expression.

Some coactivators indirectly regulate gene expression by binding to an activator and inducing a conformational change that then allows the activator to bind to the DNA enhancer or promoter sequence.Once the activator-coactivator complex binds to the enhancer,RNA polymerase 2 and other general transcription machinery are recruited to the DNA and transcription begins.

Many coactivators also function as corepressors under certain circumstances.Cofactors such as TAF1 and BTAF1 can initiate transcription in the presence of an activator(act as coactivator) and repress basal transcription in the absence of an activator(act as corepressor).

Transcriptional regulation is one of the most common ways for an organism to alter gene expression.The use of activation and coactivation allows for greater control over when,where and how much protein is produced.This enables each cell to be able to quickly respond to environment or physiological changes and helps to mitigate any damage that may occur if it were otherwise unregulated.

Activators are found in all living organisms,but coactivator proteins are typically only found in eukaryotes because they are more complex and require a more intricate mechanism for gene regulation.In eukaryotes,coactivators are usually proteins that are localized in nucleus.