Family-specific differences in transcription efficiency of Ig heavy chain promoters.

Murine Ig variable region heavy chain genes (V(H)) are grouped into families based on coding sequence homology. We observed that the accompanying promoter sequences were also conserved in a family-specific manner. Remarkably, no one has directly compared the transcription efficiencies of V(H) genes from different families. Using an in vitro transcription 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 family promoter exhibited the highest level of transcription and specifically 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 efficiency 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.