DNA-binding activity of p100, a transcriptional coactivator, to single-stranded C-rich sequences.

We have recently identified and purified six minisatellite Pc-1 binding proteins (MNBPs), which bind to mouse hypervariable minisatellite Pc-1, from nuclear extracts of NIH3T3 cells. In the present paper, we describe one of those MNBPs, MNBP-G, that binds to single-stranded d(CTGCC)n. Amino acid sequences of three proteolytic peptide fragments of MNBP-G were determined and cDNA clones isolated. MNBP-G was thereby proved identical to the transcriptional coactivator protein, p100. The mRNA was expressed ubiquitously but particularly strongly in liver, heart, and kidney. Recombinant p100 bound to single-stranded d(CTGCC)n and other C-rich sequences, such as d(CCTGCC)n, d(CTTCC)n, and d(C)n, but not to their complementary G-rich sequences or double-stranded forms. The DNA-binding ability of p100 demonstrated here suggests an involvement in transcriptional activating processing, in addition to its bridging activity between transcription factors and the basal transcription machinery reported previously.(Communicated by Tamio YAMAKAWA, M. J. A., April 14, 2003)