The nucleotide sequence on both sides of the polyketide synthase gene of the erythromycin-producing bacterium reve the presence of ten genes that are involved in L-mycarose () and D-desosamine () biosynthesis or attachment. Mutant strains carrying targeted lesions in eight of these genes indicate that three ( an ) act in L-mycairose biosynthesis or attachment, while the other five ( and ) are devoted to D-desosamine biosynthesis or attachment. The remaining two genes ( and ) appear to function in L-mycarose biosynthesis based on computer analysis an earlier genetic data. Three of these genes, and lie between the and genes on one side of the polyketide synthase genes, while the remaining seven, and lie upstream of the gene on the other side of the gene cluster. The deduced products of these genes show similarities to: aldohexos 4-ketoreductases (), aldoketo reductases (), aldohexose 5-epimerases (), the gene of the daunomycin biosynthetic pathwa of (), glycosyltransferases ( and ), the AscC 3,4-dehydratase from the ascarylose biosynthetic pathway of (), and mammalian -methyltransferases (). The gene resembles a cytochrome P450, but lacks the conserved cysteir residue responsible for coordination of the haem iron, while the gene displays no meaningful similarity to other known sequences. From the predicted function of these and other known and genes, pathways for the biosynthesis of L-mycarose and D-desosamine have been deduced.


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