High impact information on LTE1

• We also find that the presence of Tem1 and Lte1 in the bud is required for mitotic exit [1].
• Gic proteins became essential for mitotic exit when activation of the mitotic exit network through Cdc5 polo kinase and the bud cortex protein Lte1 was impaired [2].
• We found that Lte1 physically associates with Ras2-GTP both in vivo and in vitro and that the Cdc25 homology domain (CHD) of Lte1 is essential for the interaction with Ras2 [3].
• LTE1 belongs to the CDC25 family that encodes a guanine nucleotide exchange factor for GTP-binding proteins of the ras family [4].
• Previously we have shown that LTE1 is essential for termination of M phase at low temperatures [4].

Biological context of LTE1

• Unlike TEM1, LTE1 is not restricted to mitosis but is expressed throughout the cell cycle [5].
• Five eis mutants disrupted established VPS (vacuolar protein sorting) genes, The sixth, LTE1, is a Low Temperature (<15 degrees C) Essential gene encoding a large protein with potential guanine nucleotide exchange (GEF) domains [5].
• We isolated extragenic suppressors which suppress the cold sensitivity of lte1 cells and confer a temperature-sensitive phenotype on cells [6].
• Cells mutant for the suppressor alone were arrested at telophase at non-permissive temperatures and the terminal phenotype was almost identical to that of lte1 cells at non-permissive temperatures [6].
• Some of the common sequences between these two genes are also partially homologous with the amino acid sequence of LTE1, another gene of S. cerevisiae [7].

Anatomical context of LTE1

• However, the checkpoint functions without Lte1p and apparently senses cytoplasmic microtubules in the mother/bud neck [7-9] [8].

Physical interactions of LTE1

• Dominant mutant alleles of yeast protein kinase gene CDC15 suppress the lte1 defect in termination of M phase and genetically interact with CDC14 [6].
• These findings suggested the hypothesis that movement of the spindle pole through the neck allows Tem1p to interact with Lte1p, promoting GTP loading of Tem1p and mitotic exit [9].

Regulatory relationships of LTE1

• The multicopy MSI2 also suppresses the heat shock sensitivity of cells with the RAS2val19 mutation but not those with the bcy1 mutation, suggesting that the MSI2 protein may interfere with the activity of the RAS protein [10].
• Furthermore, when overexpressed, CLA4 induces Lte1 phosphorylation and localization to regions of polarized growth [11].
• Here we investigate how Ras, and the Cdc42 effector Cla4 regulate the localization of Lte1 [12].

Other interactions of LTE1

• The genetic interaction among LTE1, TEM1, and CDC15 indicates that they cooperatively play an essential role for termination of M phase [4].
• The cdc15 mutations thus isolated were recessive with regard to the temperature-sensitive phenotype and were dominant with respect to suppression of lte1 [6].
• We have identified MSI2 as a gene of Saccharomyces cerevisiae which, when on a multicopy vector, suppresses the heat shock sensitivity caused by the loss of the IRA1 product, a negative regulator of the RAS protein [10].
• Following spindle checkpoint activation, the cell cycle phosphorylation of Bfa1 and Lte1 is protracted and some species are accentuated [13].
• Temporal coupling of spindle disassembly and cytokinesis is disrupted by deletion of LTE1 in budding yeast [14].

References