* Loading: The first amino acid is activated with ATP as a mixed acyl-phosphoric acid anhydride with AMP by the A-domain and loaded onto the serine-attached 4-phospho-pantethine (4PP) sidechain of the PCP-domain catalyzed by the PCP-domain (thiolation).
* Some A domains require interaction with MbtH-like proteins for their activity.
* Sometimes the amino group of the bound amino acid is formylated by an F-domain or methylated by an NMT-domain.