Molecular machines encoded by bacterially-derived multi-domain gene fusions that potentially synthesize, N-methylate and transfer long chain polyamines in diatoms

Silica glass formation in diatoms requires the biosynthesis of unusual, very long chain polyamines (LCPA) composed of iterated aminopropyl units. Diatoms processively synthesize LCPA, N-methylate the amine groups and transfer concatenated, N-dimethylated aminopropyl groups to silaffin proteins. Here I show that diatom genomes possess signal peptide-containing gene fusions of bacterially-derived polyamine biosynthetic enzymes S-adenosylmethionine decarboxylase (AdoMetDC) and an aminopropyltransferase, sometimes fused to a eukaryotic histone N-methyltransferase domain, that potentially synthesize and N-methylate LCPA. Fusions of similar, alternatively configured domains but with a catalytically dead AdoMetDC and in one case a Tudor domain, may N-dimethylate and transfer multiple aminopropyl unit polyamines onto silaffin proteins.

► Diatoms contain bacterially-derived polyamine biosynthetic gene fusions.
► The fusion proteins may potentially synthesize very long chain polyamines.
► Chromatin protein modification domains have been recruited to the fusion proteins.
► The chromatin modification SET domains may N-methylate the long chain polyamines.
► Some fusion proteins may transfer polyamines to silaffin proteins for glass formation.