SQV-8 is similar to a glucuronyltransferase. (A) Cosmid ZK1307 and plasmid clones assayed for sqv-8 rescue activity. + indicates that three or more independently transformed lines con tained rescued sqv-8 animals; − indicates that five or more independently transformed lines contained no rescued sqv-8 animals. Underlined restriction sites are unique in the region of the cosmid that is depicted in detail (i.e., the region from EagI to SacI). The open arrowhead indicates the site at which a frame-shifting insert was introduced, and the vertical line in the bottom clone indicates the site from which this insert was precisely removed. (B) Alignment of the SQV-8, GlcAT-P, and GlcAT-I protein sequences as well as protein sequences predicted from a schistosomal cDNA, and six C. elegans ORFs (W07G9.A, T09E11.1, T15D6.7, C54C8.5, C47F8.4, and E03H4.12) predicted by the Genome Sequencing Consortium. Identities between SQV-8 and any other protein are boxed in black. N-terminal identities are not indicated, because they seem likely to occur randomly in this region. Three or more identical residues that are not shared with SQV-8 are boxed in gray (in some cases two different sets of three identities are in gray within a single column). The underlined amino acids were predicted by the algorithm of (54) (using spans of seven) to have positive hydropathy and therefore may be contained within transmembrane domains. Other stretches of positive hydropathy occur within the regions of amino acid similarity but are not consistently conserved and so are not indicated. The predicted change in amino acid sequence caused by each mutant sqv-8 allele is indicated directly above the amino acid affected, and the DNA sequence of mutant stop codons is noted in parentheses. Cys-317 of GlcAT-P is indicated by a black arrowhead. The region of the alignment from SQV-8 amino acid positions 156–189 is bracketed underneath (see text).

SQV-3 is similar to members of a glycosyltransferase family. (A) Cosmid C47F11 and plasmid clones assayed for sqv-3 rescue activity. Symbols are used as in Fig. 1A. (B) Alignment of the SQV-3, GalT, GlcNAcT, and partial human N-acetylgalactosaminyltransferase (GalNAcT) protein sequences and a C. elegans protein sequence, W02B12.11, predicted by the Genome Sequencing Consortium. Identities, transmembrane domains, and predicted changes in mutant alleles are indicated as in Fig. 1B. Open arrowheads indicate Tyr and Trp residues in GalT implicated in binding GlcNAc and/or UDP-Gal, the black arrowhead indicates a Trp residue in GalT required for catalytic activity, and the gray arrowhead indicates a GalT Tyr residue that can be replaced by Phe without affecting catalytic activity (43). The long version of GalT is shown, and the initiator methionine of the short version is circled.

SQV-7 is similar to LPG2, a protein required for GDP-mannose transport. (A) Cosmid C52E12 and plasmid clones assayed for sqv-7 rescue activity. + indicates that two or more independently transformed lines contained rescued sqv-7 animals. Otherwise symbols are used as in Fig. 1A. (B) Alignment of the SQV-7 and Leishmania LPG2 protein sequences and protein sequences predicted from two human cDNAs. Human 1 is predicted from cDNA accession no. D87449, and human 2 from clone 132056 (see text). The human 2 cDNA is likely to be incomplete at its 5′ end, which is indicated by three dots at the human 2 N terminus. Identities and predicted changes in mutant alleles are indicated as in Fig. 1B. (C) Kyte-Doolittle hydropathy plots of SQV-7 and Leishmania LPG2. In each case, the amino acid sequence is plotted along the horizontal axis, and its corresponding hydropathy (54) is plotted along the vertical axis. Regions above the central horizontal line are of positive hydropathy and, if sufficient length, therefore may be contained within transmembrane domains. The two plots are drawn at the same scale.

A model for sqv gene function. SQV-3, SQV-7, and SQV-8 may catalyze the formation of an oligosaccharide on one or more glycoproteins, glycolipids, or proteoglycans. The oval represents a glycoprotein, glycolipid, or proteoglycan, the longer straight line an oligosaccharide of unspecified structure, and the shorter straight lines sugar-sugar linkages. The biochemical activities proposed for SQV-3, SQV-7, and SQV-8 are based on a subset of those defined for the proteins related to them in amino acid sequence (see text). The terminal oligosaccharide is depicted as an unsulfated version of the HNK-1 epitope but instead may be less closely related to this epitope, may be further modified by the addition of sugars and/or sulfate groups, or may occur as a repeating rather than terminal unit (see text).