A virus produces a protein X that activates only a few of the virus’s own genes

Question

A virus produces a protein X that activates only a few of the virus’s own genes (V1, V2, and V3) when it infects cells. The cellular proteins A (a zinc finger protein) and the cellular protein B (a homeodomain protein) are known to be repressors of the viral genes V1, V2, and V3. You examine the complete upstream gene regulatory sequences of these three viral genes and find that:

1. V1 and V2 contain binding sites for the zinc finger protein A only.
2. V3 contains a binding site for the homeodomain protein B only.
3. The only sequence that all three genes have in common is the TATA box.

Label each one of the choices below as LIKELY or UNLIKELY to be an explanation for your findings. For each choice you label as UNLIKELY, explain why


__________ A. Protein X binds nonspecifically to the DNA upstream of V1, V2, and V3 and activates transcription.
__________ B. Protein X binds to a repressor and prevents the repressor from binding upstream of V1, V2, and V3.
__________ C. Protein X activates transcription by binding to the TATA box.
__________ D. Protein X activates transcription by binding to and sequestering protein A and protein B.
__________ E. Protein X represses transcription of the genes for proteins A and B.

Explanation / Answer

A. Protein X binds nonspecifically to the DNA upstream of V1, V2, and V3 and activates transcription : 3. The only sequence that all three genes have in common is the TATA box. It is likely because the RNA polymerase by binding at promoter region initiate the transcription of genes.

B. Protein X binds to a repressor and prevents the repressor from binding upstream of V1, V2, and V3: It is likely because the protein A and protein B are cellular proteins having binding sites for viral genes and repress their expression.

C. Protein X activates transcription by binding to the TATA box: It is unlikely because the protein A is cellular protein having binding sites for viral genes V1 and V2 and repress their expression.

D. Protein X activates transcription by binding to and sequestering protein A and protein B: It is unlikely because proteins A and B are repressors that inactivate V1, V2 and V3 viral genes.

E. Protein X represses transcription of the genes for proteins A and B : It is unlikely because the cellular proteins A and B repress viral proteins.

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