UNUSUAL GENE ORGANIZATION IN THE PROTOZOAN PARASITE ENTAMOEBA-HISTOLYTICA

We have analyzed three independent genomic loci of the protozoan paras ite Entamoeba histolytica that contain coding regions for the iron-con taining superoxide dismutase, the pore-forming peptide, and the galact ose-inhibitable lectin. All of the three structural genes were found t o be closely linked unidirectionally to other coding sequences. The in tergenic regions did not exceed 1,350 nucleotides. Nuclear run-on data demonstrated that at least the galactose-inhibitable lectin gene is t ranscribed in a monocistronic fashion. Comparison of the genomic seque nces described here with several others reported previously for E. his tolytica revealed a number of invariable peculiarities for the gene or ganization of this parasite: (i) Coding sequences are not interrupted by introns; (ii) 5' untranslated regions are rather short and transcri ption starts at the consensus sequences ATTCA of ATCA; (iii) an unusua l TATA-motif is located about 30 nucleotides upstream of the start of transcription and comprises the sequence TATTTAAA, which reveals prote in binding activity as determined by gel retardation assays; (iv) the conserved pentanucleotide motif TA(A)/TTT is found within the relative ly short 3' untranslated regions and functions putatively as the trans cription termination signal; and (v) a stretch of up to 12 pyrmidine r esidues is located at the end of transcribed sequences.