GENE AMPLIFICATION IN ENTAMOEBA-HISTOLYTICA

We show here data suggesting that Entamoeba histolytica, the protozoan responsible for human amebiasis, presents DNA amplification in a fash ion similar to that described for transformed mammalian cells, By tran smission electron microscopy (TEM), we found linear, circular and conc entric circular DNA molecules exhibiting the main events of the unsche duled DNA amplification process. Loops were formed after the recombina tion of two nonadjacent DNA regions, and bubbles appeared from the rec ombinant strands without involving the looped-out sequences, Bubbles g rew up and underwent further replication rounds to produce a nested se t of partially replicated circles. Multicircle complexes were also for med from putative replication origin without recombination of distant DNA regions, Clones derived from the strain HM1:IMSS exhibited differe nt DNA contents, suggesting DNA amplification. The parental clone A an d its daughter clone C2 differed in rDNA gene copy numbers, but this w as observed only when total DNA was separated by pulse field gel elect rophoresis, and no significant differences were detected in nuclear DN A. The dissection of the events observed by TEM led us to propose an o nion skin model for gene amplification in E. histolytica.