Identification of sites for distinct DNA binding proteins including Oct-1 and Oct-2 in the Cr2 gene

The murine Cr2 gene produces two distinct products in a variety of murine cell types. Both of these transcripts appear to initiate from the same position within the gene but vary from one another via an alternative splicing event within the coding exons. An analysis of those gene sequences that might control the cell specific expression of the Cr2 gene has identified a region of Cr2 5' of the transcription start site that is conserved in both the murine Cr2 and human CR2 genes. When this region was examined using the gel shift assay with nuclear extracts from cells expressing Cr2 (B cells) and those that do not (T cells and fibroblasts), at least four distinct proteins were identified that bound to at least three distinct sites. The DNA sequence recognized by two of these proteins is the octamer sequence recognized by a family of transcriptional regulators including the B cell specific Oct-2 protein. During an acute bacterial infection, the levels of Oct-2 and Cr2 mRNA are both depressed. This suggests that the Oct-2 protein directly controls the transcriptional activity of the Cr2 gene and that during such an infection, the levels of Ag receptors on B cells (Ig and complement receptors) are diminished.