Cloning of type XVII collagen. Complementary and genomic DNA sequences of mouse 180-kilodalton bullous pemphigoid antigen (BPAG2) predict an interrupted collagenous domain, a transmembrane segment, and unusual features in the 5'-end of the gene and the 3'-untranslated region of the mRNA

Abstract

Thus far, 16 distinct vertebrate collagens (types I-XVI) have been delineated. In this study, we have cloned a mouse collagenous protein, the 180-kDa bullous pemphigoid antigen (BPAG2). Isolation of over-lapping clones, together with 5' and 3' rapid amplification of cDNA ends, allowed delineation of the entire coding sequence. The 5' and 3' ends of the mRNA transcripts were confirmed by primer extension and anchored reverse transcription polymerase chain reaction analyses. The deduced polypeptide contained 1,433 amino acids, including a collagenous domain that consisted of 13 separate segments. Computer analysis of the deduced amino acid sequence demonstrated the presence of a membrane-associated segment. Examination of the 5' end of the BPAG2 gene revealed that the 295-base pair (bp) exon 1 contained two segments of (T)13AA and TT(A)11, whereas exon 2 was shown to contain the translation initiation codon. The 3' end of the mRNA transcript identified two 6-bp inverted repeat sequences that could form a stem for a 30-bp hairpin loop followed by a series of U residues. Comparison of mouse and human BPAG2 sequences demonstrated 86% homology and the unit of evolutionary period of 4.2 million years. In summary, we have cloned full-length mouse BPAG2 cDNA sequences that encode a collagenous polypeptide. We propose that this polypeptide be designated as the alpha 1-chain of type XVII collagen.