Duplicated gene clusters suggest an interplay of glycogen and trehalose metabolism during sequential stages of aerial mycelium development in Streptomyces coelicolor A3(2)

DNA sequencing and operon disruption experiments indicate that the genes gl gBI and glgBII, which code for the two developmentally specific glycogen br anching enzymes of Streptomyces coelicolor A3(2) each form part of larger d uplicated operons consisting of at least four genes in the order pep1-treS- pep2-glgB. The sequences of the TreS proteins are 73% identical (93% simila r) to that of an enzyme that converts maltose into trehalose in Pimelobacte r, a distantly related actinomycete; and the Pep1 proteins show relatedness to the alpha-amylase superfamily. Disruptions of each operon have spatiall y specific effects on the nature of glycogen deposits, as assessed by elect ron microscopy. Upstream of the glgBI operon, and diverging from it, is a g ene (glgP) that encodes a protein resembling glycogen phosphorylase from Th ermatoga maritima and a homologue in Mycobacterium tuberculosis. These thre e proteins form a distinctive subgroup compared with glycogen phosphorylase s from most other bacteria, which more closely resemble the enzymes from eu karyotes. Diverging from the glgBII operon, and separated from the pep1 gen e by two very small ORFs, is a gene (glgX) encoding a probable glycogen deb ranching enzyme. It is suggested that most of these gene products participa te in the developmentally modulated interconversion of immobile, inert glyc ogen reservoirs, and diffusible forms of carbon, both metabolically active (e.g. glucose-l-phosphate generated by glycogen phosphorylase) and metaboli cally inert but physiologically significant (trehalose).