Although cellulose synthase sequences within closely related bacterial groups (e.g., within y-proteobacteria or actinobacteria) generally display relatively high sequence conservation, they are often divergent when compared across phyla. Examination of sequenced genomes reveals the presence of alternative gene clusters that coincide with the sequence divergence of various groups of cellulose synthases. Such novel gene organizations exist in cyanobacteria, actinobacteria, chloroflexales, as well as proteobacteria and, unlike the Group I and II gene clusters described above, gene organizations are conserved across phyla. The characterization of novel gene organizations has the potential to inform current knowledge of the components necessary for cellulose biosynthesis, broaden our definitions of what constitutes cellulose, and ultimately provide a map of routes taken by organisms to utilize the P-1,4-homopolymer.
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