1. In hippogriffs, the Talon gene, that is required for claws to form, is only e
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1. In hippogriffs, the Talon gene, that is required for claws to form, is only expressed in the toes of the animal In trying to understand how transcription is regulated in fantastic beasts, we have been analyzing the expression of the Talon gene. In the diagram below is the sequence of transcribed is an A, underlined in the sequence below. Two other sequences in this region are also underlined the Talon promoter, where the first nucleotide Below the sequence (labeled a-f) are diagrams representing the wild-type promoter (a), and several mutants that were tested for their ability to initiate transcription. Variants b through f either contain small deletions (b-d) or point mutations (e, f). At the right are indicated the relative levels of transcription for each variant, measured in arbitrary Units TGCTGACGAGCTGATGCTGCaTG.3 Relative gene activity 10 Units 4 Units 2 Units 0 Units 20 Units 2 Units a. For constructs b-f indicate: what promoter sequence element might be affected, and explain why the expression level is changed to the extent shownExplanation / Answer
In construct ‘b’ GC box is missing. This is essential to start transcription or you can say it is essential for initiation of transcription. Although TATA box is there, yet the absence of GC box leads to low gene expression (4 units).
RNA polymerase binds to the TATA box to initiate transcription. In construct ‘c’ the TATA box is not there. So, RNA polymerase has no place to bind. Therefore, gene expression is lowest (2 units).
In construct ‘d’ GC box and TATA box, both are absent. So, gene expression is totally lost (0 units).
In construct ‘e’ a point mutation occurs at the start of TATA box. Note that the perfect TATA box sequence is TATAAT. When ‘G’ is mutated to ‘T’, then then perfect sequence is formed. With the perfect promoter, the enhancer ‘A’ lying downstream (see near the 3’ site) is attached. This gives enhanced gene expression which is double the parent gene i.e. 20 units.
In construct ‘f’ the TATA box sequence is hampered. Enhancer will not be able to bind to this. Binding of RNA polymerase will also not be perfect. So, the gene expression is low (only 2 units).
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