Which statement is true regarding nuclear transport signals?

Nuclear transport signals play a critical role in the movement of proteins between the nucleus and the cytoplasm. These signals are unique stretches of amino acid sequences that are recognized by specific transport receptors, allowing for selective entry and exit of proteins from the nucleus. The specificity for transport proteins means that only proteins with the appropriate nuclear localization signals (NLS) are effectively recognized and transported, ensuring that essential proteins reach their functional destinations while preventing the passage of non-specific molecules. This selective mechanism is vital for maintaining cellular functions and regulation, as it allows the cell to control which proteins reside in the nucleus.

In contrast, other statements imply inaccuracies about the universality and exclusivity of these signals in other types of cells and proteins. For example, nuclear transport signals are not exclusive to all eukaryotic cells, nor are they found in every single protein, and they are certainly not limited to mitochondrial proteins, which have separate transport mechanisms.