TI - Involvement of conserved serine 8 (Ser8) in Zfra-induced apoptosis . AB - Ser8 is a conserved PHOSphorylation site in Zfra [10] . We determined the potential role of this site in conferring the apoptotic function of Zfra . By site -directed mutagenesis , Ser8 was altered to Gly ( S8G ) . L929 cells were electroporated with EGFP-Zfra , S8G or EGFP , and the cells were cultured for 48 hr . Again , transiently overexpressed Zfra induced death of L929 cells ( 348 + - 86% ; n = 8 ) , whereas S8G mutant had a significantly reduced activity in causing cell death ( 171 + - 56% ; n = 8 ) ( Figure 2 ) . These observations suggest that Ser8 PHOSphorylation is essential for Zfra -induced apoptosis .