- Ser6 in the maize actin-depolymerizing factor, ZmADF3, is phosphorylated by a calcium-stimulated protein kinase and is essential for the control of functional activity. Smertenko, A.P., Jiang, C.J., Simmons, N.J., Weeds, A.G., Davies, D.R., Hussey, P.J. Plant J. (1998)