Background: Id proteins not only regulate cell differentiation negatively, but they also promote growth and apoptosis. To know the mechanism of how Id regulates cell fate, we previously isolated an Id-associating protein, MIDA1, which positively regulates cell growth. Its predicted amino acid sequence contains tryptophan-mediated repeats (Tryp-med repeats) similar to the DNA binding region of the c-Myb oncoprotein. We determined whether MIDA1 can bind to DNA in a sequence specific manner by PCR-assisted binding site selection.
Results: We identified a 7-base sequence (GTCAAGC) surrounded by a 1-3 bp palindromic sequence as the DNA sequence recognized by the Tryp-med repeats of MIDA1. This motif is located within the 5'-flanking sequence of several growth regulating genes. Gel shift assays revealed that this sequence and a certain length of flanking DNA are necessary for MIDA1 to bind DNA in a stable manner. Methylation interference and DNase I footprint analysis suggested that the DNA binding of MIDA1 is resistant to DNA methylation and that MIDA1 does not specifically localize on this particular motif.
Conclusions: We concluded that MIDA1 is a novel sequence-specific DNA binding protein with some different properties from the usual transcription factors and that MIDA1 may act as a mediator of Id-mediated growth-promoting function through its DNA binding activity.