LIPH and tetrasomy 12p: Although trans-acting ATs andAHs can be foundas stand-alone proteins, such as PksC (AT) and PksD (AH) from thebacillaene PKS (Figure 1B), they can also occur as di- or tridomain fusions with AT-AH (e.g.,OocV), AH-AT (e.g., RhiG), AT-ER (e.g., PksE) or AH-AT-ER (e.g., OzmM)domain architectures (Figure 1C).6 Interestingly, ATs, but notAHs, can pair with a C-terminal ER domain, possibly as a result offavorable gene fusion events.