42. A new member of the RiceMutator family, generated by deletions and insertions

R. Ishikawa’, K. Miura1, M. SENDA2, S. AKADA2, T. HARADA’ and M. Niizeki1

1) Faculty of Agriculture and Life Science, Hirosaki University, 036-8561 Japan

2) Gene Research Center, Hirosaki University, 036-8561 Japan

     RiceMutator (RMu) is a transposable element of super-Mu family that includes the maize Mutator transposable element. We have cloned a 4374 bp element, RMuJ-IR36 (AB006808), which has a long ORF carrying the putative transposase domain and 193bp of terminal inverted repeats (TIRs) flanked by 9bp target site duplication. We have also cloned a 897 bp element, RMu2-1R36 (AB017542), which is a deletion derivative of RMu1- IR36. We are currently cloning all RMu family members from the rice genome to understand the nature of the RMu family and to obtain evidence for active transposition events. We tried the Inverse-PCR (I-PCR) method using a single primer starting from 1Nt to 25 nt in the left arm of RMu1-1R36. Eco RI-digested and ligated genomic DNA of the Akage strain was used as a template to amplify the Inverse-PCR product. We then cloned and sequenced these PCR products to design further primers for amplifying the respective RMu insertions. One of the insertions, 1 147bp in size, was cloned and named RMu2-IE1. It showed 74% homology to RMu2-1R36 with several base substitutions, insertions and deletions. One of these insertions was 244 bp, and part of it showed high homology to the wanderer tansposable element (Fig. 1 A and B, Ronald eta!. 1992). However, there was no wanderer TW or target site duplication (Fig. 2) and there was only part of the sequence in the right TW of the RMu element. In addition, internal tandem duplications showed homology to part of the EST sequence (Fig. 1C and D, C98506). Sequence similarities between the internal sequence of Mutator transposable elements and unrelated sequences have been reported (Bennetzen et al. 1993). One possible mechanism for recruiting an extopic sequence into Mutator elements is a gene conversion system (Hsia and Schnable 1996). We speculate that RiceMutator might also have a mechanism similar to the maize Mutator system for recruiting an unrelated genomic sequence. This mechanism would create divergent family elements within maize Mutator elements and rice RMu elements.