title: A human dihydrofolate reductase intronless pseudogene with an Alu repetitive sequence: multiple DNA insertions at a single chromosomal site.
abstract: A dihydrofolate reductase (DHFR) pseudogene, hDHFR-psi 3 has been isolated from a human genomic DNA fragment library. Sequence analysis of this gene revealed a lack of introns and the presence of a tract of nine adenines, 90 bp downstream from the end of the coding sequence. These features suggest that hDHFR-psi 3 was derived from a processed RNA molecule that has been converted into DNA and inserted into a chromosome, analogous to the origin of three intronless human DHFR genes previously described. An interesting feature of hDHFR-psi 3 is the presence of a member of the Alu moderately repetitive DNA sequence family within the DHFR coding region. This Alu element is flanked by a 16 bp directly repeated DNA segment derived from DHFR coding sequences. The Alu element apparently has been inserted into the intronless DHFR pseudogene and thus, there have been two insertions at a single chromosomal locus. The hDHFR-psi 3 contains only the 3' half of the DHFR coding sequence. Immediately upstream from the directly repeated sequence before the Alu element is an adenine-rich tract. The DNA farther upstream is moderately repetitive and is related to neither DHFR nor Alu DNA sequence. Therefore, it seems possible that a third insertion has occurred at the same site further disrupting the hDHFR coding sequences.
mesh_terms: D001483:Base Sequence; D004274:DNA, Recombinant / Q000032:analysis; D005796:Genes; D006801:Humans; D012320:RNA Polymerase III / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D004274:DNA, Recombinant; D012333:RNA, Messenger; D013762:Tetrahydrofolate Dehydrogenase; D012320:RNA Polymerase III