PRIM1 Protein, Human

PRIM1, the catalytic subunit of the DNA primase complex and a vital component of the DNA polymerase alpha complex, plays a crucial role in the initiation of DNA synthesis. During the S phase of the cell cycle, the DNA polymerase alpha complex, comprising POLA1, POLA2, PRIM1, and PRIM2, is recruited to DNA replicative forks through direct interactions with MCM10 and WDHD1. Within this complex, PRIM1 initiates DNA synthesis by oligomerizing short RNA primers on both leading and lagging strands. The primers are subsequently extended by the polymerase alpha catalytic subunit and transferred to polymerase delta and polymerase epsilon for processive synthesis on the lagging and leading strands, respectively. In the primase complex, both subunits are indispensable for the initial di-nucleotide formation, while the extension of the primer depends solely on the catalytic subunit. PRIM1 synthesizes 9-mer RNA primers, known as 'unit length' RNA primers, incorporating ribonucleotides in the presence of ribo- and deoxy-nucleotide triphosphates (rNTPs, dNTPs). The initiation of RNA primer synthesis by PRIM1 requires a template thymine or cytidine, with an adenine or guanine at its 5'-end, and exhibits binding affinity for single-stranded DNA.