Origin-defective mutants of SV40.

We have described a new technique for the isolation and propagation of nonconditionally lethal mutants. We have used this method to generate mutants of SV40 that contain a defective origin of DNA replication. Using these mutants, we have established the following: (1) SV40 DNA replication and early transcription are functionally separate. (2) A functional viral origin of DNA replication is not necessary for the maintenance of transformation. (3) The lack of the origin of SV40 DNA replication does not affect the efficiency of transformation when nonpermissive cells are transfected by DNA using the calcium technique.