This subset of the Verified Set contains proteins in which the N-terminal methionine is clipped off by methionine amino peptidase (MAP).
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.
Purified and N-terminally sequenced SecB lacks the first two amino acids but the SecB crystal structure contains the first two amino acids. Although verified as missing the first two amino acids, SecB is included in this subset of proteisn missing only the first amino acid since the Met is predicted to be clipped and the penultimate Ser residue may be clipped as a result of a proteolytic artifact.
The first 10 amino acids of PcnB are processed off by an unknown protease, but PcnB is included in this subset because it is cytoplasmic; the AUU start codon has been confirmed by mutagenesis.
The first 11 amino acids of GltB are processed off by an unknown protease, but GltB is included in this subset because it is cytoplasmic.
The first 14 aa of ClpP are proteolytically processed in trans by another ClpP molecule, but ClpP is included in this subset because it is cytoplasmic.
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