The complete primary structure of the mouse type XIII collagen chain w
as determined by cDNA cloning. Comparison of the mouse amino acid sequ
ences with the previously determined human sequences revealed a high i
dentity of 90%. Surprisingly, the mouse cDNAs extended further in the
5' direction than the previously identified human clones. The 5' seque
nces contained a new in-frame ATG codon for translation initiation whi
ch resulted in elongation of the N-terminal noncollagenous domain by 8
1 residues. These N-terminal sequences lack a typical signal sequence
but include a highly hydrophobic segment that clearly fulfills the cri
teria for a transmembrane domain. The sequence data thus unexpectedly
suggested that type XIII collagen may be located on the plasma membran
e, with a short cytosolic N-terminal portion and a long collagenous ex
tracellular portion. These sequence data prompted us to generate antip
eptide antibodies against type XIII collagen in order to study the pro
tein and its subcellular location. Western blotting of human tumor HT-
1080 cell extract revealed bands of over 180 kDa. These appeared to re
present disulfide-bonded multimeric polypeptide forms that resolved up
on reduction into 85-95-kDa bands that are likely to represent a mixtu
re of splice forms of monomelic type XIII collagen chains. These chain
s were shown to contain the predicted N-terminal extension and thus al
so the putative transmembrane segment. Immunoprecipitation of biotinyl
ated type XIII collagen from surface-labeled HT-1080 cells, subcellula
r fractionation, and immunofluorescence staining were used to demonstr
ate that type XIII collagen molecules are indeed located in the plasma
membranes of these cells.