RT Journal Article SR Electronic T1 Phosphorylation of Arp2 is not essential for Arp2/3 complex activity in fission yeast JF Life Science Alliance JO Life Sci. Alliance FD Life Science Alliance LLC SP e201800202 DO 10.26508/lsa.201800202 VO 1 IS 5 A1 Alexander E Epstein A1 Sofia Espinoza-Sanchez A1 Thomas D Pollard YR 2018 UL https://www.life-science-alliance.org/content/1/5/e201800202.abstract AB LeClaire et al presented evidence that phosphorylation of three sites on the Arp2 subunit activates the Arp2/3 complex to nucleate actin filaments. We mutated the homologous residues of Arp2 (Y198, T233, and T234) in the fission yeast genome to amino acids that preclude or mimic phosphorylation. Arp2/3 complex is essential for the viability of fission yeast, yet strains unable to phosphorylate these sites grew normally. Y198F/T233A/T234A Arp2 was only nonfunctional if GFP-tagged, as observed by LeClaire et al in Drosophila cells. Replacing both T233 and T234 with aspartic acid was lethal, suggesting that phosphorylation might be inhibitory. Nevertheless, blocking phosphorylation at these sites had the same effect as mimicking it: slowing assembly of endocytic actin patches. Mass spectrometry revealed phosphorylation at a fourth conserved Arp2 residue, Y218, but both blocking and mimicking phosphorylation of Y218 only slowed actin patch assembly slightly. Therefore, phosphorylation of Y198, T233, T234, and Y218 is not required for the activity of fission yeast Arp2/3 complex.