Complete, precise, and innocuous loss of multiple introns in the currently intronless, active cathepsin L-like genes, and inference from this event.
Retrotransposition typically generates pseudogenes. Here we demonstrate a different fate of the retro-processed genes through a novel mechanism in which the retro-processed genes still maintain their sequence intactness and the original functions. We show that the shrimp cathepsin L (CatL) gene MeCatL has lost all of its five introns. Also, ProEPB, the ancestor of the CatL-like barley EPBs and rice REP1, has lost all of its three introns. The multiple introns in a gene might have been eliminated simultaneously and precisely at the original locus for the CatL-like genes of shrimp, barley, rice, Drosophila, and Theileria. We reason that retrotransposition is not responsible for the generation of a processed active intronless (PAI) gene when the gene product retains its sequence intactness and its original function. We propose that double-strand-break repair (DSBR) machinery might play a role in cDNA-mediated homologous recombination (cDMHR) that causes the loss of introns. The cDMHR/DSBR pathway is probably a fundamental mechanism for intron loss in PAI genes and in some asymmetric-intron genes.
Hu
Ke-Jin
KJ
Department of Zoology, The University of Hong Kong, Pokfulam Road, Hong Kong, China. huka@graduate.hku.hk
Leung
Pak-Chow
PC
D000595:Amino Acid Sequence; D000818:Animals; D056668:Cathepsin L; D002403:Cathepsins / Q000737:chemistry / Q000235:genetics*; D003445:Crustacea / Q000201:enzymology; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000235:genetics*; D004249:DNA Damage; D004260:DNA Repair; D017353:Gene Deletion; D001467:Hordeum / Q000201:enzymology; D007438:Introns; D008969:Molecular Sequence Data; D012275:Oryza / Q000201:enzymology; D010802:Phylogeny; D011995:Recombination, Genetic; D017386:Sequence Homology, Amino Acid
D002403:Cathepsins; D003546:Cysteine Endopeptidases; D056668:Cathepsin L