Replication and expression of thymidine kinase and human globin genes microinjected into mouse fibroblasts.

A mixture of two recombinant plasmids was microinjected into mouse thymidine kinase-negative fibroblasts (L cells). One plasmid contained the thymidine kinase gene of herpes simplex virus type I and the other contained the human beta globin gene. Seven fibroblast colonies arising from injected cells incubated in hypoxanthine/aminopterin/thymidine medium were analyzed. These microinjected cells were shown to: (i) produce functionally active herpes simplex type I thymidine kinase enzyme, (ii) replicate the human beta globin gene, and (iii) produce human beta globin mRNA sequences at low levels. Thus, the genetic defect (lack of thymidine kinase activity) was corrected by the microinjected thymidine kinase gene, and a coinjected human beta globin gene was replicated and weakly expressed.