A conserved sequence in the immunoglobulin J_κ–C_κ intron: possible enhancer element

Abstract

Several functionally important genetic elements (such as the TATA box, mRNA splice sequences, poly(A) addition signal) were first detected as short segments of unexplained sequence homology within non-coding regions of different genes. A short region of unknown sequence in the intron between the human J_κ and C_κ immunoglobulin coding regions was found to be sufficiently homologous to the corresponding segment of the mouse gene to form stable heteroduplexes¹. Although no specific function has yet been definitely ascribed to this region (which we call the kappa intron conserved region, or KICR), some functional significance has been inferred from the findings that (1) activation of B lymphocytes induces a DNase hypersensitivity site in this region^2,3 and (2) deletions including this region reduce expression of κ genes introduced into lymphoid cells⁴. To delineate the KICR more precisely and to test the generality of the sequence conservation in a third species, we have sequenced this region of the human and mouse genes and have examined the corresponding region of a recently cloned rabbit κ gene. We find a segment of about 130 base pairs (bp) that shows striking conservation in all three, species, demonstrating homology significantly higher than within the C_κ coding region itself. Two short sequences from the J_κ–C_κ intron that were noted by other investigators to be homologous to proposed ‘enhancer’ sequences both lie within the conserved region.