A VARIABLE DNA REGION OF ENTAMOEBA-HISTOLYTICA IS EXPRESSED IN SEVERAL TRANSCRIPTS WHICH DIFFER IN GENETICALLY RELATED CLONES

A highly variable DNA region (EhVR 1), isolated from Entamoeba histoly tica clone A, strain HM1:IMSS, is transcribed into several transcripts , which differ in genetically related clones. EhVR1 (3.5 kb) is compos ed of two contiguous fragments; one of these 1.9 kb long, at the 3' en d, identified similar transcripts in clones A, L6 and C2 (all derived from strain HM1:IMMS), the other of 1.6 kb, at the 5' end, detected 0. 5, 0.6 and 0.7 kb transcripts only in clone A. Variability of the 1.6 kb fragment was found even within the same clone maintained under diff erent conditions. EhVR1 was localized to 1.3 and 1.4 Mb linear chromos omes and also found in circular molecules. The sequence of the 1.6 kb fragment revealed the presence of a large number of different repeats, including inverted and palindromic repeats. A p145 sequence, previous ly detected in episomal DNA of the amoeba, was found at the 5' end of EhVR1. The presence of EhVR1 in linear and circular molecules, its hig h number of repeats, and its variability in genetically related clones suggest the existence of DNA regions that undergo dynamic non-recipro cal recombination between circular episomes and linear chromosomes, an d may thus contribute to variability in the trophozoite genome.