MOLECULAR CHARACTERIZATION OF TRANS-GOLGI P230 - A HUMAN PERIPHERAL MEMBRANE-PROTEIN ENCODED BY A GENE ON CHROMOSOME 6P12-22 CONTAINS EXTENSIVE COILED-COIL ALPHA-HELICAL DOMAINS AND A GRANIN MOTIF

Using autoantibodies from a Sjogren's syndrome patient, we have previo usly identified a 230-kDa peripheral membrane protein associated with the cytosolic face of the trans-Golgi (Kooy, J., Toh, B. H., Pettitt, J. M., Erlich, R. and Gleeson, P. A. (1992) J. Biol. Chem. 267, 20255- 20263), Here we report the molecular cloning and sequence analysis of human p230 and the localization of its gene to chromosome 6p12-22, Par tial cDNA clones, isolated from a HeLa cell cDNA library using autoant ibodies, were used to obtain additional cDNAs, which together span 769 5 base pairs (bp), The p230 mRNA is similar to 7.7 kilobases. Two alte rnatively spliced mRNAs for p230 were detected, These differed by 21- and 63-bp insertions in the 3'-sequence, resulting in differences in a mino acid sequence at the carboxyl terminus, The predicted 261-kDa pro tein is highly hydrophilic with 17-20% homology with many proteins con taining coiled-coil domains, Apart from two proline-rich regions (amin o acids 1-117 and 239-270), p230 contains a very high frequency of hep tad repeats, characteristic of alpha-helices that form dimeric coiled- coil structures, p230 also includes the sequence ESLALEELEL (amino aci ds 538-546), a motif found in the granin family of acidic proteins pre sent in secretory granules of neuroendocrine cells, This is the first report of a cytosolic Golgi protein containing a granin motif. The str uctural characteristics of p230 indicate that it may play a role in ve sicular transport from the trans-Golgi.