Ime1 is the upstream activator of a transcriptional cascade of
sporulation-specific genes involved in different steps of meiosis and
plays a pivotal role in the initiation ofmeiosis in Saccharomyces cerevisiae
(1–4). The IME1 promoter is repressed by glucose and nitrogen and is
induced in the presence of acetate (5,6). Nitrogen starvation and acetate
as the sole carbon source are themost efficient and common nutritional
conditions to induce meiosis in S. cerevisiae (7).
G1 cyclins block the Ime1 pathway to inhibit meiosis by downregulating
IME1 transcription and preventing Ime1 accumulation
within the nucleus (8). The mechanism of downregulating IME1
transcription by G1 cyclins has been analyzed in detail: Cln3 represses
the expression of IME1 via Swi6 and Cln2 (9). Cln levels normally
decrease when cells cease growth (10,11), and this decrease is
necessary for the initiation of meiosis (12). Kyokai no. 7 (K7), which is
a sake yeast strain (S. cerevisiae) (13), barely sporulates. In K7 cells,
CLN3 mRNA and protein are not downregulated under sporulation
conditions and it has been demonstrated that deletion of the G1 cyclin
gene CLN3, a key activator of the cell cycle, allows K7 cells to induce
IME1 transcription and sporulate under sporulation conditions (14).
Thus, Cln3 is involved in the mechanism underlying sporulation
incompetence in K7 cells.
The TOR (target of rapamycin) pathway is involved in the cellular
response to the changes in nitrogen and carbon source (15–18). There
are two functionally distinct TOR complexes in S. cerevisiae. One of
them, TOR complex I (TORC1), is the target of the immunosuppressive
Ime1 is the upstream activator of a transcriptional cascade ofsporulation-specific genes involved in different steps of meiosis andplays a pivotal role in the initiation ofmeiosis in Saccharomyces cerevisiae(1–4). The IME1 promoter is repressed by glucose and nitrogen and isinduced in the presence of acetate (5,6). Nitrogen starvation and acetateas the sole carbon source are themost efficient and common nutritionalconditions to induce meiosis in S. cerevisiae (7).G1 cyclins block the Ime1 pathway to inhibit meiosis by downregulatingIME1 transcription and preventing Ime1 accumulationwithin the nucleus (8). The mechanism of downregulating IME1transcription by G1 cyclins has been analyzed in detail: Cln3 repressesthe expression of IME1 via Swi6 and Cln2 (9). Cln levels normallydecrease when cells cease growth (10,11), and this decrease isnecessary for the initiation of meiosis (12). Kyokai no. 7 (K7), which isa sake yeast strain (S. cerevisiae) (13), barely sporulates. In K7 cells,CLN3 mRNA and protein are not downregulated under sporulationconditions and it has been demonstrated that deletion of the G1 cyclingene CLN3, a key activator of the cell cycle, allows K7 cells to induceIME1 transcription and sporulate under sporulation conditions (14).Thus, Cln3 is involved in the mechanism underlying sporulationincompetence in K7 cells.The TOR (target of rapamycin) pathway is involved in the cellularตอบสนองต่อการเปลี่ยนแปลงในแหล่งไนโตรเจนและคาร์บอน (15-18) มีมีสองหน้าที่แตก TOR คอมเพล็กซ์ใน S. cerevisiae หนึ่งพวกเขา TOR ซับซ้อนผม (TORC1), เป็นเป้าหมายของการภูมิคุ้มกัน
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