Mammalian Mcm2/4/6/7 complex forms a toroidal structure.
BACKGROUND
The Mcm proteins are a family of six homologous proteins (Mcm2-7) that play an important role in DNA replication. They form Mcm4/6/7 and Mcm2/4/6/7 complexes, but their structures are not known.


RESULTS
We found that the human Mcm2/4/6/7 tetramer forms a toroidal structure, with a central cavity about 3-4 nm in diameter. Observations were made using electron microscopy, employing the image analysis of single particles. The most predominant averaged image displayed a toroid harbouring four bulges forming corners, one of which was larger than the others. This structure was very similar to the mouse Mcm2/4/6/7 tetramer that was independently prepared and analysed by electron microscopy. These toroidal structures are distinct from that of the Mcm4/6/7 hexamer, which was also examined by electron microscopy. GST(glutathione S-transferase)-pull down and two hybrid experiments suggest that a putative Mcm6-Mcm6 hinge contributes to the formation of the Mcm7/4/6/6/4/7 heterohexamer.


CONCLUSIONS
The Mcm2/4/6/7 tetramer forms a toroidal structure that is distinct from that of the Mcm4/6/7 hexamer in size and shape.
Yabuta
Norikazu
N
Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Kajimura
Naoko
N
Mayanagi
Kouta
K
Sato
Michio
M
Gotow
Takahito
T
Uchiyama
Yasuo
Y
Ishimi
Yukio
Y
Nojima
Hiroshi
H
D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D002868:Chromosomal Proteins, Non-Histone; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D064111:Minichromosome Maintenance Complex Component 2; D064148:Minichromosome Maintenance Complex Component 4; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D011233:Precipitin Tests; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D020798:Two-Hybrid System Techniques
D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D005982:Glutathione Transferase; C099243:MCM4 protein, human; C491207:MCM6 protein, S cerevisiae; C103258:MCM6 protein, human; C491088:MCM7 protein, S cerevisiae; C101624:MCM7 protein, human; C491205:Mcm6 protein, mouse; C491086:Mcm7 protein, mouse; D064111:Minichromosome Maintenance Complex Component 2; D064148:Minichromosome Maintenance Complex Component 4; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7