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 non-specifically to the DNA upstream of V1, V2, and V3 and activates transcription. UNLIKELY.

It is unlikely that protein X binds non-specifically to the region upstream and activates the transcription. The protein X can act as a transcription factor and bind specifically to TATA box to activate all 3 proteins namely V1, V2 and V3. TATA box sequence is the only DNA sequence common to genes of all 3 proteins –V1, V2 and V3 hence binding of protein X has to be specific.

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

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