Question

You are working on a research project involving a novel transcription factor that regulates gene expression specifically in muscle cells (called MUSC1). You have already done an experiment where you showed that the addition of MUSC1 to muscle cells in culture greatly increased the expression of both actin and myosin (contractile proteins in muscle cells). Answer the following questions below:

Is MUSC1 a general or regulatory transcription factor? Explain your answer.

What two specific components would you expect MUSC1 to have as part of its protein structure?

Briefly describe the two main ways in which MUSC1 could act to stimulate transcription of actin and myosin

Describe an experiment that you could perform to demonstrate that MUSC1 binds to the promoter/enhancer region of actin and myosin genes.

A potential nuclear localization signal has been identified within the protein sequence of the transcription factor MUSC1. What experiments would you perform to demonstrate that this sequence is both necessary and sufficient for nuclear localization?

MUSC1’s entry into the nucleus is regulated so that it only goes into the nucleus to regulate the expression of contractile proteins at the correct time. Describe one mechanism by which this type of regulation can occur in the cell.

Answer 1

Answer:

a):

• A general transcription factor is always required to be bound to the promoter for RNA polymerase to work, regardless of the gene.
• But in this case, MUSC1 is only for actin and myosin producing genes (specifically in muscle cells) so this is a regulatory transcription factor.

b):

• It will have a DNA binding domain that binds, specifically, to a DNA sequence.
• They also have a Trans activating domain, which binds to the other coregulators, say for example p53 etc.

c):

• MUSC1 could bind to the core promoter , located generally in the vicinity of the transcription start site and cause the normal assembly of transcription to take place at a "basal" rate.
• It could alternatively be binding to DNA sequences located away from core promoter called proximal control elements like GC box, CAAT box, which might be causing increased transcription

d):

• we can experimentally start clipping DNA upstream of transcription start site.
• If the transcription of actin and myosin reduces drastically (checked by radiolabelled probes) we will confirm that MUSC1 binds to promoter region.

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