Question

Based on the figure, how do you think each of the four proteins function in the cell?

mature mRNA A | 1 | 2 | 3 4 | 6 | 7 | 8 | 9 | 10 | mature mRNAB | 1 | 2 | 3 | 4 NEN 6 7 8 9 10 mature minacC1 | 2 | 3 | 4 | 6 | 7 | 8 | 10 | mature mRNA D 1 2 3 4 NN 6178 10 KTS KTS NH3+ repression activation COO- Transcription regulatory domains DNA-binding domain Figure 2a. The WC1 gene includes a promoter, 10 exons, and the KTS region that can be inserted into exon 9. The KTS region reduces but does not eliminate the protein's ability to bind to specific regulatory sequences of other genes. Figure 2b. Four possible mature mRNA molecules of WC1. Figure 2c. One of the WC1 proteins translated from mature mRNA molecules: Transcription Factor D. Please answer the following question: Though only one protein product is shown in the figure, each of the four mature mRNAs are translated into protein. Based on the figure, how do you think each of the four proteins function in the cell? To receive full credit, you MUST provide a possible function for all four proteins (A, B, C, and D).

Answer 1

All four proteins are transcription factors with different levels of functioning.

Exon 1 codes for the repression domain, which all four of them have. All four of them also have the DNA binding domain coded by exons 7,8,9,10. Thus all of them can bind to regulatory sequence of some gene and prevent its expression. Proteins B and D only have exon 5, which is the activation domain. Proteins C and D have the KTS region which causes reduced binding affinity.

Possible functions of the proteins:

Protein A : A transcription factor that binds strongly to the regulatory sequence and causes repression of expression of genes. (presence of repression and DNA binding domain, no activation domain, no KTS region)

Protein B : A transcription factor that binds strongly to the regulatory sequence of specific genes. It acts as a switch with two modes- activation mode and repression mode. Thus in one condition it acts as an transcriptional activator and at certain other condition it acts as transcriptional repressor. (presence of activation, repression, DNA binding domain, no KTS region)

Protein C : A transcription factor that binds weakly to the regulatory sequence and causes repression of expression of genes. (presence of repression and DNA binding domain, no activation domain, KTS region present)

Protein D : A transcription factor that binds weakly to the regulatory sequence of specific genes. It acts as a switch with two modes- activation mode and repression mode. Thus in one condition it acts as an transcriptional activator and at certain other condition it acts as transcriptional repressor. (presence of activation, repression, DNA binding domain, KTS region)