Although the evidence is still limited, a growing body of research suggests music may have beneficial effects for diseases such as Parkinson’s.
Image credit: Shutterstock/agsandrew.
New Research In
Physical Sciences
Featured Portals
Articles by Topic
Biological Sciences
Featured Portals
Articles by Topic
Contributed by Michael R. Botchan, December 10, 2014 (sent for review November 17, 2014; reviewed by Michael O’Donnell and Bruce Stillman)
Significance
Cell division control protein 45 (Cdc45), a RecJ homologue, is essential in all eukaryotes. Cdc45 functions with the replisome CMG helicase where minichromosome maintenance (Mcm2–7) proteins provide motor activity for unwinding duplex during replication. We report that the dynamic gate between Mcm subunits 2 and 5, which is essential for the initial loading of the motor, may be an Achilles heel because the leading strand may slip from its central channel in an open gate state. Studies show that the side channel formed by the Cdc45 and GINS works as a trap and guards this gate; the Recombination protein J fold is key for this activity. We propose that this new function for Cdc45 will be important for fork integrity during the S-phase in response to double-strand breaks or replication stress.
Abstract
DNA replication licensing is now understood to be the pathway that leads to the assembly of double hexamers of minichromosome maintenance (Mcm2–7) at origin sites. Cell division control protein 45 (Cdc45) and GINS proteins activate the latent Mcm2–7 helicase by inducing allosteric changes through binding, forming a Cdc45/Mcm2-7/GINS (CMG) complex that is competent to unwind duplex DNA. The CMG has an active gate between subunits Mcm2 and Mcm5 that opens and closes in response to nucleotide binding. The consequences of inappropriate Mcm2/5 gate actuation and the role of a side channel formed between GINS/Cdc45 and the outer edge of the Mcm2–7 ring for unwinding have remained unexplored. Here we uncover a novel function for Cdc45. Cross-linking studies trace the path of the DNA with the CMG complex at a fork junction between duplex and single strands with the bound CMG in an open or closed gate conformation. In the closed state, the lagging strand does not pass through the side channel, but in the open state, the leading strand surprisingly interacts with Cdc45. Mutations in the recombination protein J fold of Cdc45 that ablate this interaction diminish helicase activity. These data indicate that Cdc45 serves as a shield to guard against occasional slippage of the leading strand from the core channel.
Footnotes
↵1T.P. and J.J.P. contributed equally to this work.
- ↵2To whom correspondence may be addressed. Email: mbotchan{at}berkeley.edu or jmberger{at}jhmi.edu.
Author contributions: T.P., J.J.P., A.C., J.M.B., and M.R.B. designed research; T.P., J.J.P., and A.C. performed research; J.L. and Z.W. contributed new reagents/analytic tools; T.P., J.J.P., A.C., J.M.B., and M.R.B. analyzed data; and T.P., J.M.B., and M.R.B. wrote the paper.
Reviewers: M.O., Rockefeller University; and B.S., Cold Spring Harbor Laboratory.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1422003112/-/DCSupplemental.
Cdc45 as the guardian of the Mcm2/5 gate
Sign up for Article Alerts
Article Classifications
- Biological Sciences
- Biochemistry
Jump to section
You May Also be Interested in
Biomedical communities and journals need to standardize nomenclature of gene products to enhance accuracy in scientific and public communication.
Image credit: Shutterstock/greenbutterfly.
Shapeshifting designs could have wide-ranging pharmaceutical and biomedical applications in coming years.
Image credit: Acacia Dishman/Medical College of Wisconsin.
Amanda Rodewald, Ivan Rudik, and Catherine Kling talk about the hazards of ozone pollution to birds.
CRISPR-Cas9 gene editing can improve the effectiveness of spermatogonial stem cell transplantation in mice and livestock, a study finds.
Image credit: Jon M. Oatley.