After microinjection hemimethylated DNA is converted into symmetrically methylated DNA before DNA replication.

In this investigation we analysed the maintenance methylation activity of the mammalian cell DNA methyltransferase by microinjection of hemimethylated HSV-tk DNA into thymidine kinase-negative rat 2 cells. We found that the hemimethylated DNA was efficiently converted into symmetrical methylated molecules before DNA replication. Furthermore, integration of the trans-DNA into the host genome is an early event after gene transfer.