A cDNA clone derived from Pneumocystis carinii contained an unusual sequence (GTGATG)2(ATGGTG)4(ATG)4 and many GAT repeats. It was found to encode a histidine and aspartic acid-rich protein (HARP). The complete cDNA contained an 888-bp open reading frame encoding a putative protein of 32.6 kDa. The deduced HARP protein contained 39 aspartic acid and 22 histidine residues. The genomic copy of the HARP gene (1203 bp in length) was found to contain 3 small introns of 46, 44, and 38 bp, respectively. HARP was predicted by computer programs to be a plasma membrane protein with nickel-binding activity.