Promoter activity and expression of sequences from Ti-plasmid stably maintained in mammalian cells.

Sequences of the plant-pathogenic Ti-plasmid were found to be constitutively expressed in LTK- and in HeLa-cells. Activity of the nopaline-synthase (nos) promoter in these cells was demonstrated by directing expression of G418 resistance from a connected neomycin-phosphotransferase II (NPT II) gene. Control transfections with the widely used thymidine-kinase (TK) promoter gave comparable transfection rates as found for the nos-promoter with NPT II. The function of the nos-promoter was also confirmed by assaying neomycin-phosphotransferase synthesized in cells containing a plasmid with the NPT II-gene under control of this promoter. Several LTK+ clones stably transfected with Ti-plasmid propagated the total Ti-plasmid DNA in a colinear state presumably as an episomal unit. Dot blot analysis and polymerase chain reaction showed predominant transcription of Ti-sequences from the T-DNA area reflecting transcriptional activity of this region not only in plant cells but also in animal cells. These results provide new information about promoter functions in systems unrelated to their natural environment.