FKBP 12 rapamycin associated protein (FRAP) is one of a family of proteins involved in cell cycle progression, DNA recombination, and DNA damage detection. In rat, it is a 235 kDa protein (symbolized RAFT 1) with significant homology to the Saccharomyces cerevisiae protein TOR 1 and has been shown to associate with the immunophilin FKBP 12 in a rapamycin-dependent fashion. The FKBP 12 rapamycin complex is known to inhibit progression through the G1 cell cycle stage by interfering with mitogenic signaling pathways involved in G1 progression in several cell types, as well as in yeast. The binding of FRAP to FKBP 12 rapamycin correlated with the ability of these ligands to inhibit cell cycle progression.