- Restoration of the biological activity of in vitro synthesized phi X DNA by transfection of ung- spheroplasts or dUTPase treatment. Baas, P.D., van Teeffelen, H.A., Teertstra, W.R., Jansz, H.S., Veeneman, G.H., van der Marel, G.A., van Boom, J.H. FEBS Lett. (1980)