Ser8 is involved in Zfra-induced apoptosis. Ser8 is a conserved phosphorylation site in Zfra . Ser8 was altered to Gly (S8G). L929 cells were electroporated with EGFP-Zfra, S8G, or EGFP, followed by culturing for 48 hr and staining with crystal violet. Transiently overexpressed Zfra induced death of L929 cells (34.8 ± 8.6%; n = 8), whereas S8G mutant had a significantly reduced activity in causing cell death (17.1 ± 5.6%; n = 8; p < 0.005, Student's t test; see *). The extent of protein expression is shown.