Hitherto it was believed ubiquitin conjugations systems were a unique possession of eukaryotes. We have recently shown that the Ub conjugation systems had their origins in prokaryotes and are widely distributed in several bacterial lineages. This bacterial system appears to have included E1 and E2-like Ub-conjugating enzymes and JAB domain peptidases. Some of them also appear to participate, like their relatives ThiS and MoaD, in sulfur incorporation reactions (in siderophore biosynthesis). In this study we also characterized a group of proteins with multiple tandem Ub-like domains that are likely to be conjugated as a “poly-ubiquitin” in certain bacteria.
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