 The O2-3 complex plays a key role in regulating actin polymerization in CD4-T cells. The ARPC-5 subunit isoforms ARPC-5 and ARPC-5-L have distinct roles in this process. ARPC-5-L is necessary for nuclear actin polymerization, while ARPC-5 is needed for cytoplasmic actin polymerization. Both subunits are important for TCR signaling, however only ARPC-5 is involved in DNA replication stress-induced nuclear actin polymerization. This article was authored by Lopamudrasadu, Nikolaos Sopulidis, M.D. Hazanouzaman, and others.