Ring A is then expanded via the polyketide synthase pathway to incorporate L-serine into ring B (figure 3). Ring A fragment is transferred from the peptidyl carrier protein (PCP) to the acyl carrier protein (ACP) by a keto-synthase (KS) domain, followed by transfer to malonyl-ACP via decarboxylative Claisen condensation catalysed by the enzyme "pigJ". This fragment is then able to react with the masked carbanion formed from the pyridoxal phosphate (PLP) mediated decarboxylation of L-serine, which cyclizes in a dehydration reaction to yield the second pyrrole ring. This intermediate is then modified by oxidation of the primary alcohol to the aldehyde, catalysed by "pigM", and methylation (which incorporates a methyl group from L-methionine onto the alcohol at the 6-position) catalysed by "pigF" and "pigN". This yields the core A-B ring structure ready for further transformations, including to the tambjamines as well as the prodiginines.