ISOLATION OF 2 NOVEL MYB-LIKE GENES FROM ARABIDOPSIS AND STUDIES ON THE DNA-BINDING PROPERTIES OF THEIR PRODUCTS

Two novel myb-like genes (atmyb6 and atmyb7) were isolated from an Ara bidopsis thaliana cDNA library. The entire proteins or the Myb domains encoded by the genes were expressed as fusion proteins in Escherichia coil. The DNA-binding domain of the murine c-Myb was also expressed i n the same way for use in comparative studies. The fusion proteins wer e examined for their DNA-binding activity using the animal c-Myb DNA-b inding site (MBS) and the binding site of the maize P gene product (PB S). The Myb domain of Atmyb6 bound to PBS more efficiently than to MBS . Complete Atmyb6 and Atmyb7 proteins preferentially bound to PBS but not MBS. This suggests that the in vitro binding consensus sequences f or both Atmyb6 and Atmyb7 are similar to PBS. The binding of the Myb d omain of Atmyb6 to both PBS and MBS raises the possibility that the pr otein recognizes multiple sequences in vivo. The third alpha-helix and three adjacent amino acids in the third repeat (R3) of c-Myb were rep laced with the analogous sequence of Atmyb6 to create a chimeric Myb p rotein. This chimeric protein bound to PBS with a low affinity but fai led to bind to MBS. Thus the binding pattern of the chimeric Myb prote in is similar to that of the Atmyb6. This result suggests that the las t 20 amino acids in the R3 repeat of Atmyb6 play a major role in DNA-b inding.