ENZYMIC TRANSFER OF RHAMNOSYL UNITS FROM THYMIDINE DIPHOSPHATE RHAMNOSE TO BACTERIAL CELL-WALL FRAGMENTS

Biosynthesis of oligosaccharide-lipid in Streptococcus sanguis

An oligosaccharide-lipid containing N-acetyl d-glucosamine (GlcNAc), l-rhamnose, and d-glucose was synthesized when the particulate enzyme from Streptococcus sanguis was incubated with UDP-GlcNAc, TDP-rhamnose, and UDP-glucose. The incorporation of d-glucose into the lipid was dependent on the preincorporation of l-rhamnose, which in turn was dependent on that of GlcNAc. This indicates that the order of sugar incorporation is GlcNAc, l-rhamnose, and d-glucose. The synthesis of GlcNAc-lipid was stimulated twofold by ATP and was inhibited strongly by UDP and slightly by UMP, CDP, and TDP, but not by all other nucleoside diphosphates and nucleoside monophosphates tested. A [gamma-(32)P]ATP labeling experiment indicated that some acceptor lipid was present in nonphosphorylated form. The acid and alkaline stabilities of the GlcNAc-lipid were similar to those of glycosyl undecaprenylphosphate, and the thin-layer chromatographic mobility of the lipid was slightly faster than that of the mannosylphosphorylundecaprenol. The molar ratio of phosphate to GlcNAc in purified GlcNAc-lipid was found to be 0.96:1. These results suggested that the GlcNAc was attached to the lipid moiety, presumably undecaprenol, by phosphodiester bonds. The incorporation of l-rhamnose into the lipid was inhibited by UDP and UMP, respectively, in a manner similar to the incorporation of GlcNAc. This suggested that the oligosaccharide was also linked to the lipid moiety by phosphodiester bonds.

Synthesis of "group polysaccharide" by membranes from Streptococcus pyogenes and its stabilized L-form

Rhamnose and N-acetylglucosamine (GlcNAc) are incorporated from thymidine 5'-diphosphorhamnose and uridine 5-diphospho-N-acetylglucosamine (UDPGlcNAc) into membrane fragments prepared from Streptococcus pyogenes but not into membrane fragements prepared from a stabilized L-form of this organism. Incorporation from TDPrhamnose is partially dependent upon UDPGlcNAc and vice versa. The oligomeric GlcNAc and rhamonose-containing products are easily extracted from membrane particles by sedimentation through detergent solutions. They are substantially extracted into methanol but not into chloroform-methanol (2:1). When product containing both radioactive rhamnose and GlcNAc is deacetylated and hydrolyzed briefy in acid, glucosaminyl rhamnose is obtained, byt not higher oligomers, suggesting that oligomer synthesis in vitro is terminated because unidentified wnzymatic requirements are not satisfied. The data are consistent with the assembly of group A-specific polysaccharide at the cellular membrane with participation of a lipoid anchor (acceptor) molecule.

Cytoplasmic label following tritiated thymidine treatment of Allium cepa L. roots. Cytochemical and electron microscope study

Tritiated thymidine routinely labels onion root cytoplasm during most of the cell cycle. One-third of this label could be cytochemically identified as DNA. The balance of the label was not RNA or a lipid, or attributable to labeled impurities in thymidine-(3)H. In electron microscope radioautographs one-third of the cytoplasmic silver grains was over organelles, presumably mitochondria and plastids. The other two-thirds of the silver grains in electron micrographs was distributed widely, 41% over ground cytoplasm and 10% over cell walls-cell membranes. Snake venom phosphodiesterase (SVDase) extracted a cytoplasmic fraction not degraded by DNase, and did not appear to extract nuclear DNA. The SVDase-extractable fraction may be DNA or a thymidine 5'-phosphoryl group in an ester linkage with another hydroxylic compound. The nature of the nonextractable fraction is considered. Possibilities discussed are: (1) technical problems such as the binding of an acid-labile nuclear DNA in the cytoplasm; (2) non-DNA, such as breakdown products, and thymine compounds other than DNA; (3) DNA, not extractable because of the nature of its binding to other compounds or because it is a "core" resistant to DNase. Until the chemical nature of this nonextractable fraction is known, cytoplasmic label following thymidine-(3)H treatment cannot necessarily be considered DNA, nor the assumption made that thymidine-(3)H exclusively labels DNA.