The present invention relates to a method for inducing an activity of a specific RNAi in eukaryotic cells, into which the TAT protein and a nucleic acid are introduced. This nucleic acid is coding for a nucleotide sequence which comprises the sense and antisense sequences of an RNAi of interest. Said sense and antisense sequences are separated by a separating nucleotide sequence, coding for a sequence which comprises at least the minimum TAR sequence which is recognised by the TAT protein. The said transcribed separating sequence and the TAT protein are forming a complex which inhibits the activity of the RNAi of interest. The RNAi activity is then induced, by removing the TAT protein