How is it possible that a protein with a nuclear localization signal (NLS) can reside within the cytoplasm of a cell until a signaling molecule causes it to move to the nucleus? The signaling molecule causes the NLS to be cleaved from the protein. The NLS on the protein is not normally exposed on its surface until the signal binds to the protein. The signal causes all nuclear pores to open at once. The signaling molecule causes microtubules to extend into the nucleus, allowing transport of the protein via vesicles. All of these are possible answers..