CLONING OF AN ALTERNATIVE FORM OF PLAKOGLOBIN (GAMMA-CATENIN) LACKINGTHE 4TH ARMADILLO REPEAT

Plakoglobin is a member of a protein family with a repeating amino aci d motif called the armadillo repeat, and is a cytoplasmic protein foun d in both adherens junctions and desmosomes. Little is known about its function, but it has been shown to form distinct complexes with cadhe rins or desmosomal cadherins, Also, plakoglobin has been shown to form a complex with APC, a tumor suppressor gene product, We have isolated a cDNA clone encoding plakoglobin by means of the polymerase chain re action (PCR) from a human transitional carcinoma cell line. The cDNA h as the same nucleotide sequence as the previously published one [Frank e et al. (1989) Proc. Natl. Acad, Sci. USA 86, 4027-4031], except that it has a deletion of 120 bp. The deleted sequence encodes the fourth armadillo repeat. Southern blot analysis of genomic DNA revealed that there is a single copy of the plakoglobin gene per haploid genome. Clo ning and sequencing of a genomic DNA fragment containing the 120-bp de letion and the surrounding sequences revealed that these sequences are encoded by a single exon sequence. PCR amplification of the genomic D NA fragment of the corresponding region excluded the possible presence of the 120-bp deletion in the gene, Therefore the variant form is mos t likely derived through alternative splicing of precursor RNA transcr ipts in an exon sequence.