The human malaria parasite P. falciparum exhibits extensive strain- dependent genetic polymorphisms in its 14 chromosomes, contributing to the significant diversity observed for this protozoan parasite. This diversity severely hampers efforts to develop effective immunoprophylactic or chemotherapeutic approaches to contain this disease agent. This proposal will address the molecular mechanisms which generate these chromosomal polymorphisms and the functional consequences of genetic variation for parasite survival. Genetic polymorphisms in P.falciparum were initially detected by pulsed- field gel analysis of intact chromosomes, indicating extensive variations in the migration of homologous chromosomes. Detailed molecular analysis of chromosomal diversity in P. falciparum has been hampered by the long- standing difficulties in the cloning of parasite DNA, resulting from its instability in standard bacterial hosts. Work of the past several years has succeeded in overcoming this barrier and has culminated in the stable cloning of intact P. falciparum chromosomes in yeast as artificial chromosomes (YACs). These YAC libraries have greatly facilitated the analysis of chromosomal organization. In a recent study of chromosome 2, it was determined that this chromosome is segregated into a stable central domain which is transcribed and a variable, nontranscribed region at its end. The extensive variations in chromosome length among strains (50-200 kb) are confined to the terminal telomeric and subtelomeric regions of the chromosome. The current proposal will characterize: l) the structural organization of the subtelomeric domains and their function, 2) three classes of polymorphisms (breakage and healing, translocation and insertion) which account for chromosome 2 variation, 3) the generality of the chromosomal domain structure for other P. falciparum chromosomes and 4) the functional consequences of these genetic variations on gene regulation and recombination.
