Assembly of Mcm2-7 complex at ORC, in conjunction with Cdt1





Molecular weight

58 kDa (Sc); 61 kDa (Xl)

Biochemical properties


•Shows sequence similarity to Orc1

•ATP binding (ATPase not detected) (1) in yeast but in humans weak  Atpase  reported (2)

•DNA binding ds>ss  suggested to bind via minor groove (3) (note: Others suggest DNA binding through orc only and cdc6 increases ORC DNA binding specificity (4) )

• In mammals cdc6 can load downstream replication proteins to plasmid (5)



•AAA+ ATPase


•Winged helix repressor DNA-binding


•NLS – 2 (6)


•NES (6)

Protein interactions


•Orc1 (7) (8) orc stimulates cdc6 ATPase to break interaction (9)

•Cdc28 (10) (1) ( role in localizing cdc28? (8) )

•MCM2 (may not be direct) (11)

•Sir2 (3/4 less) genetic suppression (12)

•Cdc4 (13)



•Rum (partial genetic suppression) (14)

•Cdk kinase (direct) (15) (16) (17)

•ORC, Mcm2-7 (18)

• rad26 (19)



•ORC – (independent phosphorylation) (6) , possible contact ORC1 (2)

•PCNA (indirect) (20)

•Myc (21)

• pp2A regulatory subunit ( role in regulating levels (22)

TTC4 (23)




•Phosphorylation - 6 cdk sites  all can be modified ith no effects (24)




•Phosphorylation - multiple cdk sites. Needed for nuclear export (6) , needed for initiation ?  FOR (2) AGAINST (6) (25)

•phosphorylation needed for export (26) (25)





Cellular location and expression


•Protein present small window during G1 (27) (7)

•Proteolysis controlled by phosphorylation (7) and ubiquitination via the proteosome – multiple pathways:

a)   early G1 independent scf –

b)   late g1/s (dependent scf/fast)

c)    g2/m (dependent scf/ slow) (28) (29)

Degradation in cytoplasm (30) , although (31) says in nucleus.

•Chromatin binding narrow window G1/S (32) , or M - G1/S (1)



• Protein present M - g1/s (33) . Also controlled phosphorylation, ubiquitination and proteasome (34)



•In extracts on and off chromatin rapidly then loads again as Mcm2-7 come off, •Phosphorylation not involved in dissociation but ubiquitination seems to be (35)

•Phosphorylation needed for export (36)



•Seems to be always nuclear (37)



•Protein level constant in cell cycle (6)

Some breakdown via proteosome in G1 (stable g2/m) needs Cdh1/APC.

•Role phosphorylation not clear AGAINST (38) FOR (39) . Latter also suggests that although

phosphorylation is on chromatin only soluble cdc6 is broken down.

•proposed replacement of old cdc6 in the cytoplasm by newly synthesised (40)

•role for cyclin e in controlling cdc6 stability. (41)

• always present on chromatin but soluble only visible in S and M (6) (42)

• note that difference in patterns of endogenous and overexpressed. This is dependent on a particular phosphorylation (43)

• on differentiation levels decrease before cdt1,mcms and ORC but after geminin (44)

• broken down on MMS treatment via HUWE (45)  

 needs p21 (46)

• broken down after re replication via huwe not apc (47)



• overexpression associated with endoreduplication (48)


Other comments


•May contribute to mitotic exit by inhibiting CDKs (49)

• suggested role in silencing (50)

• suggested stabilises apc (51)



•Very high overexpression causes re replication (differs from SC) (52) , lower levels needed if co-express cdt1 (53)

• needed to maintain hu block via ATR/rad3/rad26 (19) some effects related to changes in rDNA repeats (54)

• transcriptional control (55)



 • second cdc6 with n terminal extension (56) suggest swop correlates with change in origin usage.

•Needed to activate chk1 in presence aphidicolin (57)



• absent in quiescent cells.

•E2f site upstream (58) which seems to be needed for suppression in quiescent cells (59)

•broken down in apoptosis (60) (61) (62)

•decreases on treatment with ionising radiation. (63) needs p53, phosphorylation and proteosome.

•affects expression ink4p16 (64)

• suggested role in G2/M regulation

(65)   S/G2/M regulation (66)

• breakdown on UV via Huwe1 (67)



•Some only have 1 protein for Cdc6/Orc1. Some eg sulfolobus solfataricus have 3 Cdc6/Orc like proteins (68)



• cul4 promotes nuclear export (69)

Revised by


Last edited

9 July 09



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