Pseudogenes of the human HPRT1 gene.

Entrez Gene lists four HPRT1 gene pseudogenes (HPRTP1, HPRTP2, HPRTP3, and HPRTP4) mapping to chromosomes 3, 5, 11q, and 11q, respectively, as originally reported by Patel et al. in 1984 (Patel PI, et al. 1984 Somat Cell Mol Genet 10:483-493). However, the Entrez Gene reports for three of the four pseudogenes (HPRTP1, HPRTP3, and HPRTP4) are currently empty. A BLAST search of both GenBank (Homo sapiens) and the human genome found the chromosome 5 associated HPRTP2 sequence and a single chromosome 11q sequence (HPRTP3 or HPRTP4?). This chromosome 11 sequence had a unique 7.2 kb insert, which may explain why it originally appeared to be two separate pseudogenes. No evidence of a chromosome 3 associated sequence was found; however, a sequence highly homologous to HPRT1 was located on chromosome 4. All of these sequences are intronless processed pseudogenes. Lastly, a sequence highly homologous to HPRT1 exon 8 was found on chromosome 10. This homologous sequence was exactly exon 8 of a gene designated PRTFDC1, for phosphoribosyl transferase domain containing 1. This gene with unknown function is almost completely homologous to HPRT1 in exon structure (except for a 21 bp (seven amino acid) insertion in exon 1) and 68% homologous in amino acid sequence.