Biology subjects

Zaher, M. S.

Publications and source records attributed to Zaher, M. S..

2 recordsLinked to original sources

bioRxiv2026

Dissecting the role of PCNA and Pif1 in replication of individual DNA molecules by DNA polymerase δ.

PCNA loading and stabilization at primer-template junctions is crucial for processive DNA synthesis by replicative polymerases. It is also essential for strand displacement synthesis during Break Induced Replication (BIR). In this study, we employed a single molecule approach to directly visualize the role of PCNA, DNA polymerase {delta} and the Pif1 DNA helicase in these pathways. We first dissected the preferential loading of PCNA by RFC to 3-junctions of gaps, nicks and flapped substrates. Moreover, we found that Pol {delta} and Pif1 both stabilize loaded PCNA and reduce its diffusion coefficient along DNA. We further show that the interaction of PCNA with Pol {delta} is essential for gap-filling synthesis. On a 5-flapped substrate, we show that both Pol {delta} and Pif1 are required for strand displacement synthesis, while PCNA is not; although, it stimulates the process.

biochemistry↗

bioRxiv2019

Structure of the processive human Pol δ holoenzyme

In eukaryotes, DNA polymerase {delta} (Pol {delta}) bound to the proliferating cell nuclear antigen (PCNA) replicates the lagging strand and cooperates with flap endonuclease 1 (FEN1) to process the Okazaki fragments for their ligation. We present the high-resolution cryo-EM structure of the human processive Pol {delta}-DNA-PCNA complex in the absence and presence of FEN1. Pol {delta} is anchored to one of the three PCNA monomers through the C-terminal domain of the catalytic subunit. The catalytic core sits on top of PCNA in an open configuration while the regulatory subunits project laterally. This arrangement allows PCNA to thread and stabilize the DNA exiting the catalytic cleft and recruit FEN1 to one unoccupied monomer in a toolbelt fashion. Alternative holoenzyme conformations reveal important functional interactions that maintain PCNA orientation during synthesis. This work sheds light on the structural basis of Pol {delta}s activity in replicating the human genome.

biochemistry↗