The biosynthesis of oxytetracycline begins with the utilization of PKS enzymes ketosynthase (KS), the chain length factor (CLF), the acyl carrier protein (ACP), and an acyltransferase (encoded as "OxyA", "OxyB", "OxyC" and "OxyP" in the oxytetracycline gene cluster) to catalyze the extension of the malonamyl-CoA starting unit with 8 malonyl-CoA extender units.