Primer Utilization by DNA Polymerase α-Primase Is Influenced by Its Interaction with Mcm10p

Abstract

Models of DNA replication in yeast andMuch progress has been made identifying proteins that assemble during early stages in replication prior to the start of DNA synthesis. These events are directed by origins of replication, which orchestrate formation of the pre-replication complex (pre-RC) 1 at origins during the G 1 phase of the cell cycle. They include origin binding by the origin recognition complex and subsequent recruitment of Cdc6 and Cdt1, followed by the loading of the Mcm2-7 complex (1, 2). Further progression is regulated by the cell cycle through the activation of two S phase promoting kinases, the S phase cyclin-dependent kinase and Cdc7/Dbf4 kinase. Activation of the pre-RC by these kinases promotes Cdc45 association with origins (3, 4), events that lead subsequently to DNA unwinding and the ordered assembly of the replication fork machinery.The DNA polymerase ␣-primase (pol ␣-primase) complex also plays an essential role in initiation by synthesizing short RNA primers required to begin both leading and lagging strand DNA synthesis. The four subunit structure of pol ␣-primase is conserved, and each subunit is essential for cell viability in yeast (5, 6). The largest subunit of pol ␣-primase (p180) contains the DNA polymerase catalytic center (7) and elongates RNA primers of 8 -12 nucleotides synthesized by primase. The catalytic center of primase is located within the p48 subunit (8), which exists as a tight complex with p58 (9, 10). The p58 subunit was shown to be required for distinct aspects of primer synthesis, including initiation and elongation (11). The fourth subunit of DNA pol ␣-primase, p70/␤, is suggested to recruit the complex onto chromatin as a result of its cell cycle-regulated phosphorylated state (12, 13). Polymerase ␣-primase subunits have been reported to interact with a number of replication proteins including Cdc45 (14), Dna2 (15), RPA (16,17), and viral initiator proteins (16,18,19), consistent with the idea that replication forks are large precisely assembled multiprotein complexes.Mcm10p has been implicated both in the initiation and elongation steps of DNA replication. MCM10 was first identified in Saccharomyces cerevisiae using screens for mutants defective in DNA replication and for the stable maintenance of plasmids (20,21). Initiation at replication origins is drastically reduced in the mcm10-1 mutant, and replication across origins is impeded (21,22). Mutations in MCM10 result in a delay in the completion of DNA synthesis after cells are released from HU arrest (23), suggesting that Mcm10p is essential for continued fork progression. MCM10 mutants are suppressed by mutant MCM5 and MCM7 genes and are synthetically lethal with mutant genes of ORC, CDC45, DNA2, DPB11, and genes encoding subunits of DNA polymerase ␦ and ⑀ (22-27). Seven new mutants named slm1-slm6 for synthetically lethal with mcm10 include mutations in genes that are allelic to MCM7, MCM2, CDC45, DNA2, and mutations in novel DNA repair genes represented by SLM2 and SLM6 (28). Biochemical and genetic int...

Human Mcm10 Regulates the Catalytic Subunit of DNA Polymerase-α and Prevents DNA Damage during Replication

“…Consistent with this hypothesis, we have recently reported that the core of Mcm10 in S. cerevisiae contains an OB-fold domain , which mediates binding to ssDNA (Fien et al, 2004). This OB-fold domain is evolutionarily conserved, and it could allow human Mcm10 to bind to the lagging stand template, facilitating Okazaki fragment initiation by pol-␣/primase.…”

“…Our data support the idea that pol-␣ is in a complex with Mcm10 ( Figure 5). Therefor, it is conceivable that Mcm10 interacts directly with the catalytic subunit, as shown for S. pombe Mcm10 (Fien et al, 2004). In budding yeast, a hydrophobic stretch similar to a domain in the mobile loop of Hsp10 is required to stabilize the catalytic subunit of pol-␣, Cdc17/Pol1 .…”

“…Mcm10 has a central oligonucleotide/ oligosaccharide binding (OB)-fold , a signature motif of RNA-and single-stranded (ss) DNA binding proteins. Thus, it is not surprising that, in vitro, Mcm10 prefers ss over double-stranded (ds) DNA (Fien et al, 2004). Within the central OB-fold resides a proliferating cell nuclear antigen (PCNA) interacting protein motif (Fien et al, 2004;Das-Bradoo et al, 2006), or PIP-box, as well as a hydrophobic stretch, similar to the one found in the mobile loop of heat-shock factor (Hsp) 10 (Ricke and .…”

“…Thus, it is not surprising that, in vitro, Mcm10 prefers ss over double-stranded (ds) DNA (Fien et al, 2004). Within the central OB-fold resides a proliferating cell nuclear antigen (PCNA) interacting protein motif (Fien et al, 2004;Das-Bradoo et al, 2006), or PIP-box, as well as a hydrophobic stretch, similar to the one found in the mobile loop of heat-shock factor (Hsp) 10 (Ricke and . Although the PIP box mediates the interaction with PCNA (Das-Bradoo et al, 2006), the Hsp10-like domain forms part of the interaction site with the catalytic subunit of DNA polymerase (pol)-␣ ( Bielinsky, 2004, 2006).…”

Physical Interactions between Mcm10, DNA, and DNA Polymerase α

“…This is a critical interaction during replication because pol ␣ is the only enzyme in eukaryotic cells that is capable of initiating DNA synthesis de novo. Indeed, Mcm10 stimulates the polymerase activity of pol ␣ in vitro (28), and interestingly, the fission yeast Mcm10, but not Xenopus Mcm10, has been shown to exhibit primase activity (29,30). Mcm10 is composed of three domains, the N-terminal (NTD), internal (ID), and C-terminal (CTD) domains (29).…”