ONLY 2 OF THE TRICHOMONAS-VAGINALIS TRIPLET AP51 ADHESINS ARE REGULATED BY IRON

The sexually transmitted parasite Trichomonas vaginalis cytoadheres to the vaginal epithelium, and four candidate trichomonad adhesins have been identified. One such protein, termed AP51, was characterized furt her. To do this, we studied a 1 kb cDNA clone (AP51.2) isolated from a phagemid expression library, which encoded a fusion protein of simila r to 38 kDa that was immuno-crossreactive with anti-AP51 serum and ret ained functional adhesive properties. We performed 5'-PCR amplificatio n to recover the missing 5' end in order to provide the complete cDNA sequence for the gene encoded by AP51.2 (ap51-2). Other PCR products r evealed almost complete sequences for two additional ap51 genes, makin g AP51 a member of a multigene family of at least three distinct prote ins and genes. The ap51-1 and ap51-3 genes each encoded for 407 amino acids while ap51-2 encoded 408 amino acids, and not unexpectedly, thes e genes had a high percent identity at the DNA and amino acid levels. Mapping confirmed the sequence distinctions and uniqueness of the thre e ap51 genes. Southern analysis using gene-specific probes revealed th e single copy nature of each of the ap51 genes, all of which were pres ent among the numerous agar clones of single trichomonads of the isola tes tested. Importantly, Northern analysis showed transcriptional regu lation by iron of only the ap51-1 and ap51-3 genes but not ap51-2, per haps indicating the presence of two bona fide isoforms of the ap51 gen es. The 3'-untranslated region of ap51-3 had a short poly (A) tail as well as the sequence motif AUUUA, which may relate to differential deg radation of ap51-3 transcripts, in comparison to ap51-1 and ap51-2. Fi nally, the ap51 genes had partial homology to the beta-subunit of succ inyl-CoA synthetase, reinforcing the idea that molecular mimicry may p lay a role in host parasitism by T. vaginalis. (C) 1998 Academic Press Limited.