T. Heinemeyer, E. Wingender, I. Reuter, H. Hermjakob, A. Kel,
O. Kel, E. Ignatieva, E. Ananko, O. Podkolodnaya, F. Kolpakov,
N. Podkolodny, and N. Kolchanov: "Databases on Transcriptional
Regulation: TRANSFAC, TRRD, and COMPEL",
Nucleic Acids Res. vol.26, pp.364-370 (1998).