Hi. In this video, we're going to be talking about an overview of eukaryotic gene regulation. The majority of the regulatory ability of the eukaryotic genome has already been discussed, as gene expression is regulated at every single step from transcription to translation. This video serves more as a review of the main points we've previously covered concerning transcription and translation. However, I want to emphasize that these regulatory mechanisms are significant forms of control over gene expression, not just sporadic events; they are purposeful in determining which genes are expressed and, consequently, the phenotype of the organism.
The first point to discuss is transcription initiation. Initiation is controlled through several factors—promoters, transcription factors that are either specialized or generalized, and DNA sequences such as enhancers, activators, and silencers. These elements are located either before or after the gene starts and can significantly influence the level of transcription and gene expression.
Let's also discuss the DNA-binding properties of transcription regulatory factors, which have specific motifs allowing them to effectively bind DNA. Some of the main DNA-binding motifs include helix-turn-helix, zinc finger, leucine zipper, and helix-loop-helix:
- Helix-turn-helix: Consists of two alpha helices connected by a turn.
- Zinc finger: A structure resembling a finger that binds a zinc ion.
- Leucine zipper: A dimer resembling the interlocking teeth of a zipper, which zips together at leucines.
- Helix-loop-helix: Similar to helix-turn-helix but connected by a loop instead of a turn.
Moreover, gene expression is further regulated through several steps involving RNA processing, stability, and translation mechanisms. For instance, RNA interference is a process utilizing small non-coding RNAs (micro RNAs or siRNAs) that degrade specific transcripts. This is particularly vital for controlling gene expression by influencing mRNA stability.
RNA processing, crucial for mRNA maturation, includes adding the 5' cap, the 3' poly A tail, and splicing. Notably, alternative splicing shifts how exons are combined, creating multiple protein isoforms from a single RNA transcript. These isoforms can result in different phenotypes, as illustrated by the sex determination in fruit flies controlled through alternative splicing of the dsx gene according to the x to autosomal ratio.
Additionally, mRNA degradation acts as a regulatory mechanism by determining mRNA lifespan. Rapidly degrading mRNA dictates a quicker cessation of protein production, effectively allowing the cell to regulate gene expression dynamically.
This presentation serves as a compact review of how specific mechanisms affect gene expression. With this understanding, we will now proceed further in our discussion.
