We also were able to identify an enhancer of the Talon gene. Like all enhancers,

Question

We also were able to identify an enhancer of the Talon gene. Like all enhancers, this DNA sequence increased the expression levels of the Talon gene. The sequence of the Talon enhancer is shown below. These factors bind to the DNA sequences 5%ATT3' (for Hippogenin) and 5,CCCGGG3, (for Griffogenin. plus four deletion mutants (h through k). Each variant was tested for its ability to help the promoter to increase The Talon gene also is regulated by two Transcription factors named Hippogenin and Griffogenin Underneath the sequence is shown the structures of five enhancer variants: the wild-type enhancer (g the transcription of the Talon gene. Relative levels of expression are shown to the right. TGATGCTactivity Relative gene 5°-AGCT GAGAATT CGCGATG CAT GGAAT TC GAGAG GAgCT ZCCArccccccaccroarcerms. 1000 Units 500 Units 500 Units 10 Units 9 _ 10 Units b. For each construct (h-k), indicate which transcription factor's ability to bind to the enhancer might be affected, and suggest why the expression level is changed to the extent shown.

Explanation / Answer

Ans. As is seen in case of (h), the vacant space is in the region 5'GAATT3' approx. The complementary transcription factor is 3'TTAA5' or, 5'AATT3'. Therefore, the complementary transcription factor affected in case of 'h' is Hippogenin.

In case of (i), similar case like h occurs. so, the complementary transcription factor affected is again Hippogenin.

In case of (j), there are two vacant spaces. These are affected by the complemantary transcription factors 5'AATT3'. As the binding of transcription factor Hippogenin is affected twice, so the mutant 'j' is an inefficient enhancer variant.

In case of (k) also, there is an important vacant spaces in the region 5'CCCGGG3'. Due to this, binding of the transcription factor Griffogenin is affected. This transcription factor has the sequence 5'CCCGGG3'. The bonding between cytosine and guanine is formed by triple hydrogen bonds compared to the double bond between adenine and thymine. So, the alteration of Griffogenin binding ability affects the construct k badly compared to Hippogenin activity. So, the mutant 'k' has become such an inefficient enhancer variant.    

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