In class we discussed how eukaryotic promoters are composed of multiple binding

Question

In class we discussed how eukaryotic promoters are composed of multiple binding sites for transcriptional regulators. Scientists can identify sequences required for the expression of a gene by monitoring the amount of mRNA (transcript below) generated from mutant promoters. The darker the band, the more mRNA is produced. Shown below is a gel showing the generation of mRNA from 18 different mutant promoters. Each band is a separate mutant where sequences were mutated in 10 base pair increments starting at -120 and going +10. PS. Ignore the two bands and just focus on the amount of total signal (intensity of dark bands)

A. From these results identify the regions that are responsible for the proper expression of the gene.

B. why do you think changing the sequence between -20 and -40 had the strongest affect?

Explanation / Answer

Eukaryotes face the same basic tasks of coordinating gene expression as do prokaryotes but in a much more intricate way. Some genes have to respond to changes in physiological conditions. Many others are parts of developmentally triggered genetic circuits that organize cells into tissues and tissues into an entire organism (except for unicellular eukaryotes). In these cases, the signals controlling gene expression are the products of developmental regulatory genes, rather than signals from the external environment.

Most eukaryotic genes are controlled at the level of transcription, and the mechanisms are similar in concept to those found for bacteria. Trans-acting regulatory proteins work through sequence-specific DNA binding to their cis-acting regulatory target sequences. Because of the much more complex regulation that is required to coordinate proper geneactivity throughout the lifetime of a multicellular organism, there are some considerable novelties as well. We shall see examples of these novelties in this and subsequent chapters.

Typically, eukaryotes have many more genes than do prokaryotes, sometimes by several orders of magnitude. The genes of higher organisms also tend to be larger, owing to the facts that cis-acting sequences on the DNA can be located tens of thousands of base pairs away from the transcription start site and that a battery of regulatory factors is sometimes needed to bring about proper regulation of certain genes.

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