Question

Consider a transcription regulatory protein that has both a nuclear localization and a nuclear export signal and is normally found both in the nucleus and in the cytosol at comparable concentrations. This protein has a high-affinity binding partner in the nucleus. Upon activation of a certain signaling pathway, the binding protein is ubiquitylated and degraded. As a result of this, ...

A. the transcription regulatory protein accumulates in the nucleus.
B. the transcription regulatory protein accumulates in the cytosol.
C. the distribution of the transcription regulatory protein does not change, but the expression of its target genes may be altered.
D. the distribution of the transcription regulatory protein does not change, and the expression of its target genes is not necessarily changed as a result of the degradation event.

Answer 1

The transcription regulatory protein will accumulate in the nucleus after its high-affinity binding partner is degraded, potentially altering the expression of target genes.

Step-by-step explanation:

When a transcription regulatory protein with both a nuclear localization signal and a nuclear export signal loses its high-affinity binding partner in the nucleus due to ubiquitylation and degradation, the regulatory protein is likely to accumulate more in the nucleus. This is because the degradation of this binding partner implies there is less retention of the transcription regulatory protein within the nucleus, thereby changing its steady-state distribution and causing it to accumulate where it has a longer half-life or is less actively exported. However, the absence of the binding partner could mean changes in the expression of the target genes, depending on whether the binding partner was an activator or repressor of the transcription regulatory protein's activity.