Substantial segments of single stranded DNA generated by stalled replication forks or resection of DNA double-strand breaks, trigger a DNA damage checkpoint response, which is dependent on activation of the PIKK-family protein kinase ATR and phosphorylation of its downstream target CHK1 mediated by their mutual interaction with CLASPIN. The RAD9-RAD1-HUS1 (9-1-1) clamp forms one half of the DNA damage checkpoint system that signals the presence of substantial regions of single-stranded DNA arising from replication fork collapse or resection of DNA double strand breaks. Loaded at the 5’-recessed end of a dsDNA-ssDNA junction by the RAD17-RFC clamp loader complex, the phosphorylated C-terminal tail of the RAD9 subunit of 9-1-1 engages with the mediator scaffold TOPBP1 which in turn activates the ATR kinase, localised through the interaction of its constitutive partner ATRIP with RPA-coated ssDNA. Here you can see the cryoEM-determined structure of a complex of the human RAD17-RFC clamp loader bound to human 9-1-1, engaged with a dsDNA-ssDNA junction. The structure answers the key questions of how RAD17 confers specificity for 9-1-1 over PCNA, and how the clamp loader specifically recognises the recessed 5’ DNA end and fixes the orientation of 9-1-1 on the ssDNA (PDB code: 7Z6H)
#molecularart ... #immolecular ... #PCNA ... #ssDNA ... #break ... #complex ... #cryoem
Structure of the complex rendered with @proteinimaging and depicted with @corelphotopaint
#molecularart ... #immolecular ... #PCNA ... #ssDNA ... #break ... #complex ... #cryoem
Structure of the complex rendered with @proteinimaging and depicted with @corelphotopaint
