BIMAAPC3, a component of the Aspergillus anaphase promoting complex/cyclosome, is required for a G2 checkpoint blocking entry into mitosis in the absence of NIMA function.
Temperature sensitive (ts) nimA mutants of Aspergillus nidulans arrest at a unique point in G2 which is post activation of CDC2. Here we show that this G2 arrest is due to loss of nimA function and that it is dependent on BIMAAPC3, a component of the anaphase promoting complex/cyclosome (APC/C). Whereas nimA single mutants arrested in G2 with decondensed chromatin and interphase microtubule arrays, nimA, bimAAPC3 double mutants arrested growth with condensed chromatin and aster-like microtubule arrays. nimA, bimAAPC3 double mutants entered mitosis with kinetics similar to bimAAPC3 single mutants and wild-type cells, indicating a checkpoint-like role for BIMAAPC3 in G2. Even cells which had been depleted for NIMA protein and which contained insignificant levels of NIMA kinase activity entered mitosis on inactivation of bimAAPC3. BIMAAPC3 was present in a >25S complex containing BIMEAPC1, and bimAAPC3 mutants were sensitive to elevated CYCLIN B expression, consistent with BIMAAPC3 being a component of the APC/C. Inactivation of bimAAPC3 had little affect on the steady state levels of the B-type cyclin, NIMECyclin B. Our results indicate that BIMAAPC3, and most likely the APC/C itself, is activated in G2 in nimA mutants. We propose that APC/C activation is part of a novel, late G2 checkpoint, which responds to a defective process or structure in nimA mutants, and which prevents inappropriate entry into mitosis.
Lies
C M
CM
Molecular and Cellular Biology Section, School of Biological Sciences, University of Kentucky, Lexington, KY 40506-0225, USA.
Cheng
J
J
James
S W
SW
Morris
N R
NR
O'Connell
M J
MJ
Mirabito
P M
PM
D000483:Alleles; D000705:Anaphase / Q000502:physiology*; D064173:Anaphase-Promoting Complex-Cyclosome; D001233:Aspergillus nidulans / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology; D016203:CDC2 Protein Kinase / Q000235:genetics; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D003470:Culture Media / Q000494:pharmacology; D019926:Cyclin B / Q000235:genetics; D000431:Ethanol / Q000494:pharmacology; D005656:Fungal Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D016195:G2 Phase / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000494:pharmacology; D008025:Ligases / Q000737:chemistry* / Q000378:metabolism; D016296:Mutagenesis / Q000502:physiology; D000072380:NIMA-Related Kinase 1; D000072379:NIMA-Related Kinases; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases
D018797:Cell Cycle Proteins; D003470:Culture Media; D019926:Cyclin B; D005656:Fungal Proteins; D009687:Nuclear Proteins; C072411:BIMA protein, Emericella nidulans; D000431:Ethanol; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases; D000072380:NIMA-Related Kinase 1; D000072379:NIMA-Related Kinases; C442331:NIMA-related kinase 6; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; D008025:Ligases; D005947:Glucose