pCEP4 is an episomal mammalian expression vector that uses the cytomegalovirus （CMV） immediate early enhancer/promoter for high level transcription of recombinant genes inserted into the multiple cloning site. The Epstein-Barr Virus replication origin （oriP） and nuclear antigen （encoded by the EBNA-1 gene） is carried by this plasmid to permit extrachromosomal replication in human, primate, and canine cells. pCEP4 also carries the hygromycin B resistance gene for stable selection in transfected cells.

pCEP4/CAT is provided as a positive control for the relative level of expression of recombinant proteins in a cell line of interest. It expresses the chloramphenicol acetyl transferase （CAT） protein from the CMV enhancer/promoter. Like its parent vector pCEP4, pCEP4/CAT contains the hygromycin B resistance gene for selection.