MOLECULAR ANALYSIS OF THE BG-RBG TRANSPOSABLE ELEMENT SYSTEM OF ZEA-MAYS L

The two components of the Bg-rbg transposable element system of maize have been cloned. The Bg element, isolated from the mutable allele wx-m32:: Bg is inserted in the intron of the Waxy (Wx) gene between exons 12 and 13. The length of the element is of 4869 bp. Bg has 5 bp terminal inverted repeats, and generates upon insertion an 8 bp direct duplication of the target sequence. Both ends of the Bg element contain a 76 bp direct repeat adjacent to the terminal inverted repeats. The hexamer motif TATCG(C)G is here repeated several times in direct or inverse orientation. The rbg element was isolated from the mutable allele o2m(r) where it is located in the promoter region of the Opaque-2 (O2) gene. rbg is approximately 4.5 kb in length, has terminal inverted repeats identical to those of the Bg element, and is also flanked by an 8 bp direct duplication at the target site. Like Bg, rbg carries the 76 bp direct repeats. Restriction enzyme analysis reveals that, compared to Bg, the receptor element is distinguishable by small deletion and insertion events. Sequence data indicate that not more than 75% homology exists at the DNA level between the rbg element and the autonomous Bg element.