Human chemotaxis receptor genes cluster at 19q13.3-13.4. Characterization of the human C5a receptor gene.

The human C5a anaphylatoxin and formyl peptide receptor genes, as well as two genes with high sequence identity to the formyl peptide receptor, FPRH1 and FPRH2, have been mapped to chromosome 19 (Lu et al., 1992). Further analysis reveals that these genes are present in the 19q13.3 band adjacent to the 13.3-13.4 interface. MRNAs for the C5a and formyl peptide receptors, as well as for FPRH1, are expressed in cAMP differentiated U937 cells and human eosinophils, while all four transcripts are expressed in human lung. This observation opens the possibility for coordinate regulation of these genes. In order to initiate the mapping of fine structure at this locus, genomic clones have been analyzed. All four of the genes have a similar structure, with the receptor protein encoded in a single exon. Detailed characterization of the C5a receptor gene reveals a two exon structure, with the 5' untranslated sequence and initiating methionine located in the first exon. An intron of approximately 9 kb separates exon 1 from the receptor-encoding exon 2. The region of genomic DNA flanking the 5' untranslated sequence possesses promoter activity when transfected into the myeloid-derived rat basophilic leukemia RBL-1 cells, but the same region is inactive when transfected into nonmyeloid cells. Deletional analyses indicate that C5a receptor 5' flanking region contains both cell-specific suppressor and promoter regions.