OCTAMER INDEPENDENT ACTIVATION OF TRANSCRIPTION FROM THE KAPPA-IMMUNOGLOBULIN GERMLINE PROMOTER

Previous analyses of immunoglobulin V region promoters has led to the discovery of a common octamer motif which is functionally important in the tissue-specific and developmentally regulated transcriptional act ivation of immunoglobulin genes, The germline promoters (K-o) located upstream of the J region gene segments of the kappa locus also contain an octamer motif (containing a single base pair mutation and referred to as the variant octamer) which has been shown previously to bind Oc t-1 and Oct-2 transcription factors in vitro. To further elucidate the role of this variant octamer motif in the regulation of germline tran scription from the unrearranged kappa locus, we have quantitated the r elative binding affinity of Oct-1 and Oct-2 for the variant octamer mo tif and determined the functional role of this octamer motif in transc riptional activation, We find that, although the variant octamer motif binds Oct-1 and Oct-2 in vitro with 5-fold lower affinity than the co nsensus octamer motif, mutation of the variant octamer motif to either a consensus octamer or non-octamer motif has no effect on transcripti onal activation from the germline promoter, We also find significant d ifferences in activation of germline and V region promoters by kappa e nhancers, Our results suggest that the germline promoters and V region promoters differ in their dependence on octamer for activation and re spond differently to enhancer activation, These findings have importan t implications in regulation of germline transcription as well as conc omitant activation of the V-J recombination of the kappa light chain l ocus.