Structure and expression of the knob-associated histidine-rich protein of Plasmodium falciparum

cDNA clones encoding 473 amino acids of the knob-associated histidine-rich protein (PfHRPI) of Plasmodium falciparum clone FCR-3/A2 (Gambia) have been isolated and sequenced. Although a short region close to the amino terminus of the predicted sequence contains three blocks of six, seven or nine consecutive histidine residues, the most abundant amino acid is lysine. The predicted sequence contains a putative amino-terminal signal sequence and two potential asparagine glycosylation sites. A 1284 bp Sau3A cDNA fragment was expressed in Escherichia coli as a fusion protein that was recognized by an anti-PfHRPI monoclonal antibody. Pulsed field gradient electrophoresis indicated that the PfHRPI gene is located on chromosome 2. The PfHRPI gene was present, apparently intact, in knobless parasites derived from one uncloned P. falciparum isolate (St. Lucia). In a knobless derivative of another uncloned isolate (Malayan Camp) and in a cloned knobless line (FCR-3/D4) of a third isolate (Gambian), that part of the gene covered by the cDNA clone has been deleted. Loss of PfHRPI expression may therefore arise via several different mechanisms of gene alteration.