Light chain promoter regions in rainbow trout Oncorhynchus mykiss: function of a classical and an atypical Ig promoter

Abstract Three rainbow trout ( Oncorhynchus mykiss ) light chain isotypes (L1, L2 and L3) have been identified at the cDNA level. Genomic clones have previously been obtained for L1 and L2, revealing different structures of the V/J/C clusters and divergent putative promoter regions. While the L1 putative promoter has a classical Ig promoter structure with TATA, E-box, and octamer, the L2 putative promoter lacks typical features of the Ig promoter. The L2 putative promoter region contains a κ-Y motif, an E-box and two putative non-consensus TATA boxes. In this study the isolation of a genomic clone that encompassed a VJC cluster of the recently described L3 isotype is described. The structure of the L3 putative promoter region is very similar to that of the L1 promoter. The transcriptional activities of the promoters of the trout L1 and L2 isotypes were compared. The promoter region of the L1 isotype showed a strong and predictable B cell-specific activity. Despite the unusual structure of the L2 V gene promoter, the transcriptional activity of it was much stronger in B-cells as compared to non B-cells. Deletion analyses of L2 promoter constructs showed that the region containing the κ-Y element is critical for the transcriptional activity of the L2 promoter. Both L1 and L2 promoters can cooperate with a B cell-specific enhancer from Atlantic cod ( Gadus morhua ).