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 transcriptio nal silencer activity can be ascribed to a minimal 150-bp fragment. Th e rearrangement silencing activity was previously shown by the replace ment of the V-J intervening sequence with a neutral DNA fragment that dramatically increased the rate of rearrangement of the transgene. Ins ertion of the minimal silencer in this neutral fragment is shown here to result in a marked decrease in rearrangement of the transgenic cons truct. Strikingly, deletion of 28 bp from the 150-bp fragment abolishe d most of the transcriptional silencing activity and had a similar eff ect on rearrangement. These results conclusively correlate the silenci ng activity on both rearrangement and transcription.