The biosynthesis of differentiation-inducing factor, a chlorinated signal molecule regulating Dictyostelium development

Differentiation-inducing factor (DIF)-1 is a chlorinated alkyl phenone released by developing Dictyostelium amoebae, which induces them to differentiate into stalk cells, A biosynthetic pathway for DIF-1 is proposed from labeling, inhibitor, and enzymological experiments, Cells incorporate Cl-36(-) into DIF-1 during development, showing that the chlorine atoms originate from chloride ions; peak incorporation is at the first finger stage, DIF-1 synthesis can be blocked by cerulenin, a polyketide synthase inhibitor, suggesting that it is made from a polyketide, This is most likely the C-12 polyketide (2,4,6-trihydroxyphenyl)-1-hexan-1-one (THPH). Feeding experiments confirm that living cells can convert THPH to DIF-1, Conversion requires both chlorination and methylation of THPH, and enzymatic activities able to do this exist in cell lysates, The chlorinating activity, assayed using Cl-36(-), is stimulated by H2O2 and requires both soluble and particulate components, It is specific for THPH and does not use this compound after O-methylation. The methyltransferase is soluble, uses S-adenosyl-L-methionine as a co-substrate, has a K-m for dichloro-THPH of about 1.1 mu M, and strongly prefers this substrate to close analogues, Both chlorinating and methyltransferase activities increase in development in parallel with DIF-1 production, and both are greatly reduced in a mutant strain that makes little DIF-1, It is proposed that DIF-1 is made by the initial assembly of a C-12 polyketide skeleton, which is then chlorinated and methylated.