The putative eukaryote-like O-GlcNAc transferase of the cyanobacterium Synechococcus elongatus PCC 7942 hydrolyzes UDP-GlcNAc and is involved in multiple cellular processes.

The posttranslational addition of a single O-linked ß-N-acetylglucosamine (O-GlcNAc) to serine or threonine residues regulates numerous metazoan cellular processes. The enzyme responsible for this modification, O-GlcNAc transferase (OGT), is conserved among a wide variety of organisms and is critical for the viability of many eukaryotes. Although OGTs with domain structures similar to those of eukaryotic OGTs are predicted for many bacterial species, the cellular roles of these OGTs are unknown. We have identified a putative OGT in the cyanobacterium Synechococcus elongatus PCC 7942 that shows active-site homology and similar domain structure to eukaryotic OGTs. An OGT deletion mutant was created and found to exhibit several phenotypes. Without agitation, mutant cells aggregate and settle out of the medium. The mutant cells have higher free inorganic phosphate levels, wider thylakoid lumen, and differential accumulation of electron-dense inclusion bodies. These phenotypes are rescued by reintroduction of the wild-type OGT but are not fully rescued by OGTs with single amino acid substitutions corresponding to mutations that reduce eukaryotic OGT activity. S. elongatus OGT purified from Escherichia coli hydrolyzed the sugar donor, UDP-GlcNAc, while the mutant OGTs that did not fully rescue the deletion mutant phenotypes had reduced or no activity. These results suggest that bacterial eukaryote-like OGTs, like their eukaryotic counterparts, influence multiple processes.

Evolution of a triplet repeat in a conifer.

The opportunity to trace the evolution of a triplet repeat is rare, especially for seed-plant lineages with a well-defined fossil record. Microsatellite PtTX2133 sequences from 18 species in 2 conifer genera were used to calibrate the birth of a CAGn repeat, from its protomicrosatellite origins to its repeat expansion. Birth occurred in the hard-pine genome ~ 136 million years ago, or 14 million generations ago, then expanded as a polymorphic triplet repeat 136-100 million years before a major North American vicariance event. Calibration of the triplet-repeat birth and expansion is supported by the shared allelic lineages among Old and New World hard pines and the shared alleles solely among North American diploxylon or hard pines. Five CAGn repeat units appeared to be the expansion threshold for Old and New World diploxylon pines. Haploxylon pine species worldwide did not undergo birth and repeat expansion, remaining monomorphic, with a single imperfect 198-bp allele. A sister genus, Picea, had only a region of cryptic simplicity, preceding a proto-microsatellite region. The polymorphic triplet repeat in hard pines is older than some long-lived microsatellites reported for reptiles, yet younger than those reported for insects. Some cautionary points are raised about phylogenetic applications for this long-lived microsatellite.