Title: Galactosyl Transferases in Mycobacterial Cell Wall Synthesis Running title: Biosynthesis of Mycobacterial Galactan

Two galactosyltransferases can apparently account for the full biosynthesis of the cell wall galactan of mycobacteria. Evidence is presented based on enzymatic incubations with purified natural and synthetic galactofuranose (Galf) acceptors that the recombinant galactofuranosyl transferase, GlfT1, from Mycobacterium smegmatis, the M. tuberculosis Rv3782 ortholog, known to be involved in the initial steps of galactan formation, harbors dual β-(1→4) and β-(1→5) Galf transferase activities and that the product of the enzyme, decaprenyl-P-P-GlcNAc-Rha-Galf-Galf, serves as a direct substrate for full polymerization catalyzed by another bifunctional Galf transferase, the GlfT2, the Rv3808c enzyme. ACC EPT ED The mycobacterial cell wall- including the essential, covalently linked complex of peptidoglycan, heteropolymeric arabinogalactan and highly hydrophobic mycolic acids- is responsible for many of the pathophysiological features of members of the Mycobacteriu