MIDA1 is a sequence specific DNA binding protein with novel DNA binding properties.

Abstract

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. 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. 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.