MOLECULAR-CLONING AND EXPRESSION OF CDNAS ENCODING HUMAN ALPHA-MANNOSIDASE-II AND A PREVIOUSLY UNRECOGNIZED ALPHA-MANNOSIDASE-IIX ISOZYME

Golgi alpha-mannosidase II (alpha-MII) is an enzyme involved in the processing of N-Linked glycans. Using a previously isolated murine cDNA clone as a probe,,ve have isolated cDNA clones encompassing the human alpha-MII cDNA open reading frame and initiated isolation of human genomic clones. During the isolation of genomic clones, genes related to that encoding alpha-MII were isolated, One such gene was found to encode an isozyme, designated alpha-MII(x). A 5-kb cDNA clone encoding alpha-MII(x) was then isolated from a human melanoma cDNA library, However, comparison between alpha-MII(x) and alpha-MII cDNAs suggested that the cloned cDNA encodes a truncated polypeptide with 796 amino acid residues, while alpha-MII consists of 1144 amino acid residues. To reevaluate the sequence of alpha-MII(x) cDNA, polymerase chain reaction (PCR) was performed with lymphocyte mRNAs, Comparison of the sequence of PCR products with the alpha-MII(x) genomic sequence revealed that alternative splicing of the alpha-MII(x) transcript can result in an additional transcript encoding a 1139-amino acid polypeptide. Northern analysis showed transcription of alpha-MII(x) in various tissues, suggesting that the alpha-MII(x) gene is a housekeeping gene. COS cells transfected with alpha-MII(x) cDNA containing the full-length open reading frame shelved an increase of alpha-mannosidase activity, The alpha-MII(x) gene was mapped to human chromosome 15q25, whereas the alpha-MII gene was mapped to 5q21-22.