Investigating the DNA Binding Properties of the Initiator Binding Protein 2 (IBP2) in Maize (Zea Mays)

The maize (Zea mays L) initiator-binding protein2 (IBP2) gene is known to encode a protein, IBP2, with promoter-binding activity. IBP2 also resembles telomere DNA-binding proteins from other plant species. Therefore, we investigated whether the IBP2 protein, a presumed transcription factor, may actually have telomere DNA-binding activity. Using Electrophoretic Mobility Shift Assay (EMSA) we found that a C-terminal sublcone of the IBP2 protein, rIBP2 Myb-Q, binds telomeric repeat DNA in vitro. We also found that rIBP2 Myb-Q binds strongly to double stranded telomere repeat sequences with three or four tandem repeats, but only weakly to sequences with two tandem repeats. Furthermore, we found no evidence of binding with a single repeat (5' TTTAGGG 3') sequence. We also found that single point changes in (T1:A and G6:T) in the three-repeat sequence diminished, but did not entirely abolish, binding activity. Additionally, we found that the rIBP2 Myb-Q did bind weakly to the initiator sequence of the Shrunken1 promoter. From these experiments, we conclude that IBP2 is likely to have telomeric functions in vivo, and possibly play a role in both gene transcription and telomere functions.