LTE1 is essential for termination of M phase at low temperatures, along with TEM1, and CDC15 (5), all part of the mitotic exit network which is an elaborate signaling system comprising at least eight essential genes: CDC5, CDC14, CDC15, DBF2, DBF20, LTE1, MOB1, and TEM1 (6, 7). LTE1 was originally discovered as a locus essential for growth at 8 C, and was named for this trait as Low Temperature Essential 1 (4). It was later inferred from sequence similarities that LTE1 must code for a guanine nucleotide exchange factor (8). Genetic evidence suggests that Lte1p activates the GTPase Tem1p which activates the protein kinase Cdc15p. Cdc15p then relieves the inhibition of the protein phosphatase Cdc14p by Net1p, thereby allowing exit from mitosis (7). In a normal cell cycle, Bub2p bound to Tem1p restrains mitotic exit until the daughter-bound centrosome (with which both Bub2p and Tem1p preferentially associate) comes into contact with Lte1p in the bud, effectively coupling mitotic exit with nuclear segregation (9). Some evidence suggests that the spatial separation of Tem1p and Lte1p is a key mechanism for controlling the timing of mitotic exit (9).

Last updated: 2002-10-17