Silencing of the paternal allele of three imprinted genes (Igf2r, Slc22a2 and 
Slc22a3) requires cis expression of the Air RNA that overlaps the promoter of 
one of them (Igf2r). Air is a non-coding RNA whose mode of action is unknown. We 
tested the role of the Igf2r promoter and the role of transcriptional overlap 
between Igf2r and Air in silencing in this cluster. We analyzed imprinted 
expression in mice in which the Igf2r promoter is replaced by a thymidine kinase 
promoter that preserves a transcription overlap with Air, and in mice with a 
deleted Igf2r promoter that lack any transcriptional overlap with Air. Imprinted 
silencing of Air, Slc22a2 and Slc22a3 is maintained by the replacement promoter 
and also in the absence of transcriptional overlap with Air. These results 
exclude a role for the Igf2r promoter and for transcriptional overlap between 
Igf2r and Air in silencing Air, Slc22a2 and Slc22a3. Although these results do 
not completely exclude a role for a double-stranded RNA silencing mechanism, 
they do allow the possibility that the Air RNA has intrinsic cis silencing 
properties.