STRUCTURE AND SUPERSTRUCTURE OF PLASMODIUM-FALCIPARUM SUBTELOMERIC REGIONS

Walking and jumping procedures were employed to obtain a consensus map of the 35-40 kb subtelomeric region shared by many chromosomal extrem ities in Plasmodium falciparum strain 3D7, and to characterise the por tions flanking the rep20 tract, which is known to contain tandemly rep eated, apparently degenerate, 21-bp repeats. The borders of rep20 were shown to harbour short (possibly locally homogenised) patterns of non -degenerate 12-, 17-, 23- and 28-bp repeats. The central repetitious p ortion of the consensus map was estimated to be about 18 kb in length, and to be separated from the telomere by approx. 11 kb of non-repetit ious sequence, maintained with high fidelity at different chromosomal ends. Several kilobases of similarly conserved, non-repetitious sequen ce flank rep20 on its proximal side. Computer analysis of the rep20 se quence suggested that a peculiar superhelical winding originates from the conservation of identical nucleotide groups in phase with the pitc h of the double helix, overcoming the effect of repeat degeneration in other positions of the 21-bp unit.