Identification of Multiple Forms of 180-kDa Ribosome Receptor in Human Cells

Herein, we describe the analysis and mapping of cDNA clones encoding variant forms of the human homolog of the canine 180-kDa ribosome receptor (pl80). One form, similar to the chicken ES/130 homolog, possesses a large uninterrupted C-terminal region composed predominantly of heptad repeats predicted to form an αhelical double-stranded coiled-coil rod. Other forms contain in addition a 10-amino acid consensus motif, NQGKKAEGAQ, repeated up to 54 times in tandem close to the N-terminus. Such repeats in canine pl80 represent a ribosome-binding domain. The cDNA hybridized to a major 6-kb transcript in all tissues examined, where very high expression was observed in tissues that carry out a high level of secretion such as pancreas, liver, and placenta. The ES130/pl80 gene was mapped to chromosome 20pl2, and a potential pseudogene appears to reside on chromosome 7. In summary, the data suggest that p 180 exists in humans in different forms because of complete removal of tandem repeats, or partial intraexonic splicing, creating different repeat lengths with potentially novel ribosome-binding characteristics.