PRIM1 (DNA primase subunit 1) is the catalytic subunit of the DNA primase complex within the DNA polymerase alpha-primase complex, playing an essential role in eukaryotic DNA replication initiation 1. During S phase, PRIM1 synthesizes short RNA primers (predominantly 9-mers) on both leading and lagging DNA strands 23. The enzyme requires template thymine or cytidine to initiate primer synthesis with adenine or guanine at the 5' end, incorporating only ribonucleotides 3. Structurally, PRIM1 functions within a heterotetrameric complex where its low substrate affinity facilitates primer handoff to polymerase alpha for processive DNA synthesis 4. At the replisome, PRIM2 positions PRIM1 directly above the lagging-strand template exit channel via direct CMG helicase binding 5. Beyond its canonical replication role, PRIM1 demonstrates unexpected oncogenic functions. Elevated PRIM1 expression correlates with poor prognosis in hepatocellular carcinoma, urothelial carcinoma, and breast carcinoma 67. In colorectal cancer, PRIM1 overexpression promotes liver metastasis by recruiting neutrophils and modulating NET formation through upregulation of chemokines CXCL8, G-CSF, and CXCL2 8. Additionally, PRIM1 emerged as a component of a 4-gene predictive signature for early-onset neonatal sepsis, suggesting broader implications in immune-related conditions 9. These findings indicate PRIM1 functions as both a critical DNA replication enzyme and an emerging cancer biomarker with immunomodulatory properties.