FAMILY-SPECIFIC DIFFERENCES IN TRANSCRIPTION EFFICIENCY OF IG HEAVY-CHAIN PROMOTERS

Murine Ig variable region heavy chain genes (V-H) are grouped into fam ilies based on coding sequence homology, We observed that the accompan ying promoter sequences were also conserved in a family-specific manne r, Remarkably, no one has directly compared the transcription efficien cies of V-H genes from different families, Using an in vitro transcrip tion system, we found that transcription efficiencies of different V-H promoters differed by as much as 70-fold, These differences could be attributed to variation in the octamer-heptamer and TATA sequences, as well as to the presence or absence of initiator elements, The J558 fa mily promoter exhibited the highest level of transcription and specifi cally interacted with an Oct-1 dimer not bound by other V-H promoters, These data suggest that differential transcription and regulation of V-H promoters could occur in vivo. The increased transcription efficie ncy of the J558 promoter relative to other V-H promoters also presents a possible explanation for the abundance of J558 sterile transcripts observed before V(H)DJ(H) rearrangement.