MudrB Function in Maize and Origin within the Grasses

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The Mutator system is a highly mutagenic family of transposable elements in maize. Mutator transposition is regulated by the MuDR class of transposons. MuDR elements encode two genes: mudrA and mudrB. The mudrA gene is the putative transposase. Although known to be a necessary component of Mu activity, the biochemical function of the mudrB gene is not known. The primary objective of this research is to elucidate the evolution and function of this gene. The mudrA gene is much more widely distributed among grasses than mudrB. Based on this, and the absence of mudrB in many apparently functional MuDR-like elements, it is hypothesized that mudrB was captured by MuDR at some point during the evolution of this transposon. To test this hypothesis, several grasses related to maize will be surveyed for the presence and composition of mudrB sequences. To investigate the function of mudrB in maize, existing derivatives that express only mudrA or only mudrB will be exploited. Experiments in which these two deletion derivatives will be combined genetically will test the hypothesis that the two can compliment each other. In addition, the derivative that lacks mudrB will be crossed to mutations that affect Mutator activity. In order to determine if mudrB can contribute to high levels of MuDR transposition in a species that lacks this gene, rice will be transformed with constitutively and inducibly expressed mudrB. Proteomic analysis of proteins binding Mu element TIRs will be employed to identify proteins involved in regulating Mu element transposition in the presence and absence of mudrA or mudrB and in the presence of mutations that affect Mutator activity. Proteomic analysis of binding of Mu termini from these mutations will also serve to identify other proteins that operate in the same pathway as the mutations that affect activity.