Isolation and characterization of a processed gene for human ceruloplasmin

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Abstract
A processed pseudogene for human ceruloplasmin has been isolated that contains DNA corresponding to the functional gene sequence encoding the carboxy-terminal 563 amino acid residues and the 3'' untranslated region. The pseudogene appears to have arisen from a processed RNA species, since intervening sequences coincident with those of the functional gene have been removed, with the exception of a short segment of intronic sequence which denotes the 5'' boundary of the pseudogene. The nucleotide sequence of the pseudogene is highly homologous (97% sequence identity) with that of the wild-type gene, suggesting that pseudogene formation was a relatively recent evolutionary event. In addition to single base substitutions, there is a large 213 base pair (bp) deletion in the pseudogene sequence which corresponds to the location of an intron-exon junction in the functional gene. A 4 bp duplication that occurs at amino acid residue 683 of the wild-type coding sequence results in a frameshift mutation and introduces a premature translational termination codon at this point. This is concordant with the inability to detect a human liver transcript corresponding to the pseudogene by nuclease S1 mapping analysis. The 3'' end of the pseudogene is characterized by a 62 bp segment composed mainly of repeated TC dinucleotides. On the basis of genomic Southern blot analysis performed under high-stringency conditions, the pseudogene that we have identified seems to comprise the only sequence in the human genome that is closely related to the wild-type gene. Using somatic cell hybridization, we have mapped the pseudogene to human chromosome 8. This differs from the site of the wild-type ceruloplasmin locus, which has been assigned to chromosome 3.