We developed a mammalian transient expression system to isolate
cDNA clones that determine
hyaluronan expression. HAS-, a mouse mammary
carcinoma mutant cell line, which is defective in
hyaluronan synthase activity, was first established and used as a recipient for the expression cloning. One cloned
cDNA that overcame the deficiency was isolated. The
cDNA termed HAS contains an open reading frame of 1749 base pairs encoding a new
protein of 583
amino acids. Homology analysis of the amino acid sequence suggests that HAS
protein is related to streptococcal
hyaluronan synthase and also to Xenopus laevis DG42
protein that was found to be homologous to bacterial
hyaluronan synthase. Expression of HAS
cDNA in HAS- cells complemented not only their mutant phenotypes such as deficient
hyaluronan-matrix deposition but also
hyaluronan synthase activity itself. Therefore, HAS
cDNA is responsible for the activity of the
hyaluronan synthase, a key
enzyme of
hyaluronan synthesis in eukaryotic cells.