SQV-7, a protein involved in Caenorhabditis elegans epithelial invagination and early embryogenesis, transports UDP-glucuronic acid, UDP-N- acetylgalactosamine, and UDP-galactose

^*Department of Molecular and Cell Biology, Boston University School of Dental Medicine, Boston, MA 02118; and ^†Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139

Edited by William S. Sly, St. Louis University School of Medicine, St. Louis, MO, and approved January 24, 2001 (received for review December 14, 2000)

Abstract

Caenorhabditis elegans sqv mutants are defective in vulval epithelial invagination and have a severe reduction in hermaphrodite fertility. The gene sqv-7 encodes a multitransmembrane hydrophobic protein resembling nucleotide sugar transporters of the Golgi membrane. A Golgi vesicle enriched fraction of Saccharomyces cerevisiae expressing SQV-7 transported UDP-glucuronic acid, UDP-N-acetylgalactosamine, and UDP-galactose (Gal) in a temperature-dependent and saturable manner. These nucleotide sugars are competitive, alternate, noncooperative substrates. The two mutant sqv-7 missense alleles resulted in a severe reduction of these three transport activities. SQV-7 did not transport CMP-sialic acid, GDP-fucose, UDP-N-acetylglucosamine, UDP-glucose, or GDP-mannose. SQV-7 is able to transport UDP-Gal in vivo, as shown by its ability to complement the phenotype of Madin-Darby canine kidney ricin resistant cells, a mammalian cell line deficient in UDP-Gal transport into the Golgi. These results demonstrate that unlike most nucleotide sugar transporters, SQV-7 can transport multiple distinct nucleotide sugars. We propose that SQV-7 translocates multiple nucleotide sugars into the Golgi lumen for the biosynthesis of glycoconjugates that play a pivotal role in development.

Footnotes

↵ ‡ To whom reprint requests should be addressed. E-mail: chirschb{at}bu.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Man,

mannose;

Fuc,

fucose;

Glu,

glucose;

SA,

sialic acid;

MDCK,

Madin-Darby canine kidney cells;

RCA,

Ricinus communis agglutinin;

RCAr,

RCA resistant;

Gal,

galactose;

GlcA,

glucuronic acid;

GalNAc,

N-acetylgalactosamine;

GlcNAc,

N-acetylglucosamine;

GAG,

glycosaminoglycan;

HA,

hemaglutinin