Mcm1 promotes replication initiation by binding specific elements at replication origins

Area of Science:

• Molecular Biology
• Yeast Genetics
• DNA Replication

Background:

• Minichromosome maintenance protein 1 (Mcm1) is essential for DNA replication initiation from autonomously replicating sequences (ARS) in yeast.
• Mutations in Mcm1, like Mcm1-1 (P97L), reduce DNA binding, leading to selective origin firing and plasmid instability.
• Flanking sequences can restore plasmid stability in Mcm1 mutants, indicating their role in Mcm1-mediated replication control.

Purpose of the Study:

• To investigate the role of Mcm1 binding sites in the differential replication efficiencies of two telomeric X ARSs (ARS120 and ARS131a) in the mcm1-1 mutant.
• To determine how Mcm1 occupancy at specific ARS elements influences replication initiation and plasmid stability.

Main Methods:

• Comparative analysis of two telomeric ARS elements (ARS120 and ARS131a) in wild-type and mcm1-1 mutant yeast strains.
• Site-directed mutagenesis to alter Mcm1 binding sites within the C domain of ARS120.
• Assessment of plasmid replication efficiency and stability in response to Mcm1 binding site modifications.

Main Results:

• ARS120, unlike ARS131a, showed efficient replication in the mcm1-1 mutant due to additional Mcm1 binding sites in its C domain.
• Mutation of a key Mcm1 binding site in ARS120's C domain reduced its replication efficiency in wild-type cells.
• Increasing the number of Mcm1 binding sites in ARS120 significantly enhanced its replication efficiency.

Conclusions:

• Threshold occupancy of Mcm1 in the C domain of telomeric ARSs is critical for efficient replication initiation.
• Mcm1 binding site number and location play a regulatory role in Saccharomyces cerevisiae origin usage during DNA replication.