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Scientists from the U.K. have identified how the proteins Sld3–Sld7 help initiate DNA replication by detecting the activated MCM2–7 helicase and recruiting Cdc45, an essential component for starting replication.

What is Helicase?

Helicase is an ATP-dependent motor enzyme/protein that unwinds double-stranded DNA (dsDNA) into two single strands. This is essential for DNA replication, repair and tranion, as the separated strands provide templates for synthesis or other molecular processes.

Role in DNA Replication

During replication, helicase attaches to DNA and moves along it using energy derived from ATP hydrolysis. It changes its conformation and separates the hydrogen-bonded DNA strands, creating a Y-shaped replication fork.

The exposed strands then serve as templates for the synthesis of complementary DNA. However, unwinding generates increasing torsional stress and twisting ahead of the replication fork. Topoisomerases resolve this problem by relieving the tension and preventing DNA from becoming excessively tangled or damaged.

Recent Finding: Sld3–Sld7 and Cdc45

The study highlights an important step in the initiation of eukaryotic DNA replication:

• MCM2–7 acts as the core replicative helicase.
• Once activated, it becomes capable of unwinding DNA.
• Sld3–Sld7 proteins detect the activated MCM2–7 helicase.
• They help recruit Cdc45 to the replication machinery.
• Cdc45, together with MCM2–7 and other factors, contributes to formation of the active CMG helicase complex, which drives DNA unwinding during replication.

Thus, the finding provides greater understanding of how cells control the precise initiation of DNA replication, an important process for accurate genome duplication.