Negative Regulation of Immunoglobulin κ Light-Chain Gene Transcription by a Short Sequence Homologous to the Murine B1 Repetitive Element

Abstract

B-cell-specific expression of the immunoglobulin κ light-chain (Ig κ) gene is in part accomplished by negative regulatory influences. Here we describe a new negatively acting element (termed κ NE) immediately upstream of the NF-κ B-binding site in the Ig κ intronic enhancer. The 27-bp κ NE sequence is conserved in the corresponding positions in the rabbit and human Ig κ genes, and the human κ NE homolog was shown to have a similar negative regulatory activity. Data base searches using the mouse κ NE sequence revealed a striking homology to murine B1 repetitive sequences. A sequence homologous to κ NE and B1 was also noted in a previously identified silencer element in the murine T-cell receptor α locus. The homologous T-cell receptor α locus sequence, but notably not a corresponding 27-bp B1 consensus sequence, showed a negative regulatory potential similar to that of κ NE. The negative effect of κ NE by itself was not cell type specific but became so when paired with its 5'-flanking sequence in the Ig κ enhancer. A short (30-bp) fragment upstream of κ NE (termed κ BS) was found to be necessary and sufficient for abolishing the negative effect of κ NE in B cells. Point mutations in a T-rich motif within the κ BS sequence allowed the transcriptional repression by κ NE to be evident in B cells as well as other cells. As suggested by this cell-independent negative activity, proteins binding to the mouse and human κ NE sequences were identified in all cell types tested.