Insertion preference of maize and rice miniature inverted repeat transposable elements as revealed by the analysis of nested elements

A 128-bp insertion into the maize waxy-B2 allele led to the discovery of To urist, a family of miniature inverted repeat transposable elements (MITEs). As a special category of nonautonomous elements, MITEs are distinguished b y their high copy number, small size, and close association with plant gene s. In maize, some Tourist elements (named Tourist-Zm) are present as adjace nt or nested insertions. To determine whether the formation of multimers is a common feature of MITEs, we performed a more thorough survey, including an estimation of the proportion of multimers, with 30.2 Mb of publicly avai lable rice genome sequence. Among the 6600 MITEs identified, > 10% were pre sent as multimers. The proportion of multimers differs for different MITE f amilies. For some MITE families, a high frequency of self-insertions was fo und. The fact that all 340 multimers are unique indicates that the multimer s are not capable of further amplification.