This subset of the Verified Set contains proteins in which the N-terminal methionine is not clipped off by methionine amino peptidase (MAP). For these unclipped proteins, the initial methionine that is retained is usually, but not always, deformylated by Def.
Non-secreted proteins may be processed by methionine amino peptidase (MAP) to remove the terminal methionine, depending on the size of the second amino acid. The N-termini must be deformylated by Def before Map can act. Sometimes the second amino acid is small and MAP could act, but apparently does not, perhaps due to sequesterization of the N-terminus in the inner membrane before Def or MAP can act on it. MAP is not present in cells in large excess and overexpressed proteins may not all get processed by MAP or Def.
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