What type of signal does a precursor protein have for mitochondrial import?

A precursor protein destined for import into the mitochondria typically contains a mitochondrial targeting signal at its N-terminal region. This signal is characterized by a highly positively charged, amphipathic alpha-helical structure that facilitates its recognition and import by the mitochondrial translocase complexes.

The N-terminal alpha-helix plays a crucial role in the interaction with the import machinery of the mitochondria, particularly with receptors on the outer mitochondrial membrane. The amphipathic nature of the alpha-helix allows it to insert into the membrane, assisting in the translocation of the precursor protein across the mitochondrion's membranes and into the mitochondrial matrix.

In contrast, the other options refer to terminal signals that are not typically associated with mitochondrial import. For instance, signals associated with a C-terminal location do not provide the necessary properties for effective mitochondrial targeting and import. Understanding the structural requirements of these targeting signals is vital for examining how proteins are sorted and localized within the cell.