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. Further, A. laidlawii has enzymes of the undecaprenyl phosphate biosynthesis pathway . Further, A. laidlawii has enzymes of the undecaprenyl phosphate biosynthesis pathway from farnesyl diphosphate, including two reactions from the terpenoid synthesis pathway (farnesyldiphosphate-trans,trans,Title Loaded From File cis-geranylgeranyl-diphosphate i-trans, poly-cis-undecaprenyl diphosphate) and one reaction from the peptidoglycan biosynthesis pathway (poly-cis-undecaprenyl diphosphate ndecaprenyl phosphate). The presence of this pathway was unexpected, as it was known that eubacteria rarely use undecaprenyl phosphate in the cell wall (5). Fatty acid biosynthesis. The composition of the A. laidlawii cell membrane differs from that of other Mollicutes (33). Themain components of its cytoplasmic membrane are glycolipids and Acholeplasma-specific lipoglycans, whereas other mycoplasmas have cholesterol as a major membrane component (33). Earlier reports showed that most Mollicutes do not have fatty acid synthesis pathways (11, 53), while the activity of enzymes from this metabolic pathway had been observed in A. laidlawii (33). The functional annotation of the A. laidlawii genome identified enzymes from the fatty acids biosynthesis pathway, except for acyl-ACP-dehydrogenase, catalyzing the dehydration of enoyl-acyl-acyl-carrier protein derivatives with a carbon chain length of 4 to 16 and a reduction of NAD to NADH. Apparently, this function is performed by an unidentified protein. This metabolic pathway was never observed in the Mollicutes. Glycerolipid, glycerophospholipid, and sphingolipid biosynthesis. Only two enzymes from the glycerolipid biosynthesis pathways were identified, acetol kinase for ATP-dependent phosphorylation of glycerin to phosphoglycerin and 1,2-diacylglycerol 3-glycosyltransferase for carrying glycosyl residue from UDP-glucose to 1,2-diacylglycerol. These enzymes have not been observed in the Phytoplasma spp., and they are not connected to other metabolic pathways in A. laidlawii (2, 37). Hence, their presence does not allow for a proper glycerolipid biosynthesis. 1,2-Diacylglycerol-3-phosphate, a product of the reaction catalyzed by 1-acylglycerol-3-phosphate O-acyltransferase, is one of the initial substrates in the cardiolipin and phosphatidyl glycerophosphate synthesis. These biosynthetic pathways are complete in the A. laidlawii genome, while they have not been described in the Phytoplasma spp. (2, 37). In addition, the A. laidlawii genome has a partial biosynthesis pathway for choline and glycerol-3-phosphate, which is absent in the Phytoplasma spp. and other Mollicutes (2, 10, 13, 37, 49, 60, 64). The sphingolipid biosynthesis in A. laidlawii is represented by two copies of sphingosine kinase: phosphorylating sphingosine to sphingosine-1-phosphate. Sphingosine-1-phosphate is one of the cytoplasmic membrane components in A. laidlawii. Nucleotide metabolism. Mollicutes are unable to synthesize nucleotides de novo (31). The metabolism of purines and pyrimidines in A. laidlawii is similar to that of other Mollicutes, but there are several differences in the interconversion and degradation of nucleotides and nucleosides. In particular, the genome contains NADP oxidoreductase and ribonucleosidetriphosphate reductase, which is not found in the Phytoplasma genomes (2, 37). The genome contains genes encoding purinenucleoside phosphorylase (transforming desoxyuridine to uracil), dCMP deaminase (converting dCMP to dUMP), cytidine deaminase (catalyzing transformation of deoxycytidine to deoxyuridine and cytidine to uridine), purine.