The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains ϳ16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.

Glycopeptides derived from NIH 3T3 fibroblasts and these cells transformed by transfection with human DNA containin? om'i ~"~m c H-ras were analyzed by 500-MHz 'H-NMR spectroscopy and binding to immobilized lectins. The cells were mc1;iholically labeled with ~-[~H]glucosamine or ~- [~H]fucose and the glycopeptides included in Bio-Gel P-10 ( M , 5000-3500) were separated into neutral and charged fractions on DEAE-cellulose. The major portion (80%) of these [3H]fucose glycopeptides from the non-transformed NIH 3T3 fibroblasts were neutral or contained one or two charged residues, whereas 90% of the glycopeptides from the transformed cells contained two or more charged residues.The structure of the predominant neutral glycopeptide from the non-transformed NIH 3T3 cells was determined by 'H-NMR spectroscopy to be tetraantennary containing terminal Galal -+ 3.This structure was verified by binding to the immobilized a-Gal-specific lectin, Grijfonia simplicijolia I and leukoagglutinating phytohemagglutinin from Phaseolus vulgaris (L-PHA), which binds certain tri-or tetraantennary glycopeptides.In contrast, the structure derived by NMR spectroscopy of one of the predominant charged glycopeptides from the transformed cells was triantennary containing terminal NeuNAca2+3 in addition to Galal+3. Fucal-thIn attempting to verify this structure by lectin-binding properties it was found that removal of NeuNAca2 + 3 reduced the affinity to L-PHA -agarose. The other major glycopeptides of the transformed cells which were more charged also cotained NeuNAca2+3 but no NeuNAca2-+6 or Galal + 3 .A tentative structure was proposed for the major glycopeptide of the first charged class from NIH 3T3 cells on the basis of lectin-binding properties and the NMR spectrum which showed, in addition to NeuNAca2+3, the presence of NeuNAca2-6 and Galal +3.On the basis of the NMR spectrum and other results, it is concluded that the presence of tetraantennary oligosaccharides are not sufficient for the transformed oligosaccharide phenotype. Rather, the tri-or tetraantennae must be sialylated in a2-3 linkage, on more than one antennae, when properties of transformation are expressed in NIH 3T3 cells. Prior to transformation the tetraantennary oligosaccharides of these cells are terminated in aGal residues, whereas after transformation a-Gal residues appear to be replaced by NeuNAca2+ 3. Thus, in this case, transformation may be accompanied by a change in the glycosyltransferases responsible for termination of the branches rather than those conferring branch configurations.

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