Effects of CDC45 mutations on DNA replication and genome stability

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Cdc45 is a key component of the CMG helicase complex, essential for DNA replication initiation and nascent strand synthesis.
• Cdc45 interacts with Mcm2-7, Psf1, Sld3, and DNA polymerase epsilon (Pol ε), playing a vital role in coordinating replication.
• Understanding Cdc45 function is critical for comprehending DNA replication processes and associated diseases.

Purpose of the Study:

• To investigate the impact of specific amino acid substitutions in Cdc45 on its interactions and DNA replication.
• To analyze the consequences of impaired Cdc45 function on DNA synthesis fidelity and mutation rates.

Main Methods:

• Site-directed mutagenesis was used to create amino acid substitutions in Cdc45, targeting interaction regions with Mcm2-7, Psf1, and Sld3.
• The effects of these mutations on DNA replication were assessed under permissive and restrictive temperature conditions.
• Mutation rates and replication error incidence were quantified in the analyzed Cdc45 mutants.

Main Results:

• Mutations in CDC45 led to defective DNA replication, including delayed synthesis under permissive conditions and failure to replicate efficiently at restrictive temperatures.
• Despite initiation defects, Cdc45 mutants could synthesize DNA under restrictive conditions after initial replication under permissive conditions.
• Impaired Cdc45 function resulted in elevated mutation rates, primarily mediated by DNA polymerase zeta (Pol ζ), and increased replication errors.

Conclusions:

• Cdc45 is essential for the initiation of DNA replication.
• Defects in Cdc45 function compromise the fidelity of nascent DNA strand synthesis, leading to increased mutations and replication errors.
• These findings highlight the critical role of Cdc45 in maintaining genomic stability and offer insights into diseases linked to CDC45 dysfunction.