Poster: Regulation of gene expression

Abs # 797: Alternative Splicing and Translational Frame Shifting Define Functional Transposases Controlling Mutator transposons in maize

Presenter:	Rudenko, George N, rudenko@stanford.edu
Authors	Rudenko, George N (A)   Walbot, Virginia  (A)
Affiliations:	(A): Stanford University

DNA transposons of Mutator family in maize are controlled by the master element MuDR. This autonomous element is composed of two convergently transcribed genes, mudrA and mudrB, separated by intergenic region and flanked by long terminal inverted repeats (TIRs). The mudrA gene encodes several forms of MURA transposase by means of alternative splicing. We demonstrate that alternative splicing of the first mudrA exon differentiates whether translation starts with ATG at position +450 resulting in MURA823 (or MURA736 when the last mudrA intron is retained) trasposase or, alternatively, ATG at position +224 could specify production of the novel MURA854 protein that has an alternative N-terminus. Surprisingly, in vivo production of MURA854 would require a translational frameshift at the novel 3’ acceptor site of the first mudrA intron at position + 466. To determine the functional role of each MURA protein in vivo we expressed them from the native TIR promoter in transgenic maize. In addition, to determine if translational frameshifting occurs, two MURA854 transgenes were constructed, one expressing a native cDNA (frameshift required) and the other is a frameshift corrected form. Both MURA823 and MUR736 transposases program somatic excisions of non-autonomous Mu elements from anthocyanin reporter alleles. However, no Mu insertion events have been observed. In contrast, we found that both MURA854 transgenes are capable of mediating both Mu element excisions and insertions, albeit at lower frequency when compared to standard Mutator lines. We hypothesize that alternative splicing and translational frame shift could represent key steps in regulation of Mutator activity and that distinct forms of MURA transposase that exist in vivo might be functionally complementary.