2 GENES ENCODING HOMOLOGOUS 70-KDA SURFACE-PROTEINS ARE PRESENT WITHIN INDIVIDUAL TROPHOZOITES OF THE BINUCLEATE PROTOZOAN PARASITE GIARDIA-INTESTINALIS

A 0.52-kb DNA sequence encoding part of a major surface antigen of Gia rdia intestinalis trophozoites has been amplified by the polymerase ch ain reaction (PCR) using primers specific for nucleotide sequences tha t are conserved between two apparently related genes, tsp11 (cloned pr eviously from the Australian G. intestinalis isolate, Ad-1) and tsa417 (cloned from the Afghanistani isolate, WB). Restriction analysis reve aled that the DNA amplified from each of seven axenic isolates of G. i ntestinalis was not homogeneous, even though the template DNA had been purified from cultures that had been established from single trophozo ites. Every isolate yielded two PCR products, whose respective cleavag e fragments corresponded to tsp11 (HindIII+, PstI-, KpnI-) and to tsa4 17 (HindIII-, PstI+, KpnI+). This was confirmed by cloning individual amplification products into the plasmid vector, pGEM-7Zf(+). The seque nce of one cloned fragment (1-P4), derived from the Ad-1 isolate, but possessing restriction sites characteristic of tsa417, exhibited 98.6% identity over 425 bp with tsa417 and only 63.8% identity with the cor responding region of tsp11. The data indicate that individual trophozo ites of all the isolates examined contain a copy of each of these homo logous genes.