PFEMP3 AND HRP1 - COEXPRESSED GENES LOCALIZED TO CHROMOSOME-2 OF PLASMODIUM-FALCIPARUM

A malarial protein, Plasmodium falciparum erythrocyte membrane protein 3 (PfEMP3), has been recently characterized as a high-molecular-mass component (approx. 315 kDa) localized to the erythrocyte membrane of k nob-bearing (K+), cytoadherent (C+) mature stages of P. falciparum-par asitized erythrocytes (PE) [Pasloske et al., Mel. Biochem. Parasitol. 59 (1993) 59-72]. Knobless (K-), non-cytoadherent (C-) parasites of th e same strain were shown to lack the PfEMP3 gene. In view of the biolo gical importance of the knobby and cytoadherent phenotypes with regard to parasite virulence, we extended the analysis of PfEMP3 and its gen e product to other K+/K- and C+/C- parasites. Previously, other studie s have shown that the malarial protein, knob-associated histidine-rich protein 1 (HRP1), is also strongly correlated with knob expression. H ere, we show that PfEMP3 and HRP1 were absent from all the K- parasite s tested, including the Pale Alto (PA) K-C+ strain. This result demons trates that PfEMP3 and HRP1 are not essential for cytoadherence. PfEMP 3 was localized to chromosome 2 of the K+ parasites, within no more th an 130 kb of HRP1, between the telomere and HRP1. Stage-specific analy sis of the mRNA for HRP1 and PfEMP3 indicated maximal transcription of the genes in ring-stage parasites, with little or no mRNA present dur ing the mature parasite stages. Analysis of PfEMP3 and HRP1 by immunof luorescence assay (IFA) revealed identical staining patterns of fixed PE at all stages of the asexual life cycle. Hence, PfEMP3 and HRP1 are adjacent to each other in chromosome 2, co-expressed temporally and t heir gene products co-localized to the PE membrane.