Negative regulation of Ig gene rearrangement by a 150-bp transcriptional silencer.

We previously showed that the V-J intervening sequence of the chicken lambda immunoglobulin locus contains a strong silencer that acts both on transcription and rearrangement. We show here that the transcriptional silencer activity can be ascribed to a minimal 150-bp fragment. The rearrangement silencing activity was previously shown by the replacement of the V-J intervening sequence with a neutral DNA fragment that dramatically increased the rate of rearrangement of the transgene. Insertion of the minimal silencer in this neutral fragment is shown here to result in a marked decrease in rearrangement of the transgenic construct. Strikingly, deletion of 28 bp from the 150-bp fragment abolished most of the transcriptional silencing activity and had a similar effect on rearrangement. These results conclusively correlate the silencing activity on both rearrangement and transcription.