Pyret, a Ty3/Gypsy retrotransposon in Magnaporthe grisea contains an extradomain between the nucleocapsid and protease domains

A novel Ty3/Gypsy retrotransposon, named Pyret, was identified in the plant pathogenic fungus Magnaporthe grisea (anamorph Pyricularia oryzae). Pyret- related elements were distributed in a wide range of Pyricularia isolates f rom various gramineous plants. The Pyret element is 7250 bp in length with a 475 bp LTR and one conceptual ORF. The ORF contains seven nonsense mutati ons in the reading frame, indicating that the Pyret clone is lightly degene rate. Comparative domain analysis among retroelements revealed that Pyret e xhibits an extra domain (WCCH domain) beyond the basic components of LTR re trotransposons. The WCCH domain consists of similar to 300 amino acids and is located downstream of the nucleocapsid domain. The WCCH domain is so nam ed because it contains two repeats of a characteristic amino acid sequence, W-X-2-C-X-4-C-X-2-H-X-3-K. A WCCH motif-like sequence is found in the prec oat protein of some geminiviruses, viral RNA-dependent RNA polymerase and a lso in an Arabidopsis protein of unknown function. Interestingly, detailed sequence analysis of the gag protein revealed that Pyret, as well as some o ther chromodomain-containing LTR retrotransposons, displays significant seq uence homology with members of the gammaretroviruses (MLV-related retroviru ses) in the capsid and nucleocapsid domains. This suggests that chromodomai n-containing LTR retrotransposons and gammaretroviruses may share a common ancestor with the gag protein.