Human CR2 has a restricted cellular distribution, being expressed on B lymphocytes, dendritic cells of the spleen, pharyngeal epithelial cells, and at low levels on some T lymphocytes. CR2 is expressed by mature B lymphocytes, but not by pre-B cells or by plasma cells, suggesting that mechanisms exist for positive and negative regulation of CR2 gene expression during B cell development. S1 nuclease digestion and primer extension analysis positioned the transcriptional start site between 92 and 94 bp upstream of the ATG codon. Nucleotide sequence analysis identified several sequences within the CR2 promoter region with homology to other known promoter sequences. These included a site similar to an AP-1 site, a sequence with 10 of 13 nucleotides identical to the X box of class II genes, and a TATA box. Genomic DNA starting immediately 5' of the sequence encoding the CR2 signal peptide was subcloned upstream of the bacterial chloramphenicol acetyltransferase gene for analysis of functional promoter and enhancer sites. The functional boundaries of the CR2 promoter were determined by deletion analysis, with both the X box-like sequences and the TATA box required for CR2 expression. This analysis revealed sequences with regulatory effects on CR2 gene expression, however, these transcriptional controlling sequences did not act in a tissue specific fashion.

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