44. Putative transposase-like domain found in rice genome Ryuji ishikawa and M. freeling

1 ) Department of Plant Biology, University of California, Berkeley, CA 94720, USA 2) Faculty of Agriculture, Hirosaki University, Hirosaki 036, Japan

 The Mutator system in maize has been already known as a powerful tool for transposon tagging genes and as a unique characteristic as plant transposon. We have already found a homolog in rice genome probed with a part of MuDR which is known as regulatory element of Mutator family.

Rice genomic library originating Iroin IR36 was probed with a part of mudrA protein coding region, corresponding to a putative transposase domain homologous to that of bacterial transposons (Eisen et al. 1993). We cloned one recombinant phage probed with HindIII-HindIII region of mudrA coding sequence, which was subcloned into a plasmid called as pEH 7 as a 5.4kb length plasmid shown as Fig. 1. Sequence data around PstI-XhoI region showed high homology to the putative transposase domain.

Fig. 1. Structure of regulatory element of Mu family, MuDR and similarity of rice homologs of the putative transposase domain of MuDR at amino acidic level. Similarity revealed only by same amino acids is shown by intensity of filled color, other parts filled with white has not been compared yet in the pEH7 plasmid. Exactly there is 426bp core region of the domain as ORF. The homology is 69% at nucleic acids level and 64% at amino acids level to the putative tranposase domain of MuDR. The homology was estimated as 80% with substitutional amino residues. The flanking sequence so far examined showed slightly lower homology which would be due to the genetic distance between maize and rice among monocots (Fig. 1 ). More further flanking region expected as terminal inverted region is being sequenced.

Southern hybridization data showed that there are at least 3 copies in a cultivated rice (AA genome) when genomic DNA was digested by SacI which cannot cut inside of the used probe (PstI-XhoI fragment). Some RFLPs were also detected between different cultivars such as Indica and Japonica cultivars, and among different kinds of wild genomes of Oryza genus (data not shown).

References

Eisen J.A., M.B. Benito and V. Walbot, 1993. Sequence similarity of putative transposases links the maize Mutator autonomous element and a group of bacterial insertion sequences. Nucleic Acids Research 22: 2634-2636.