MOLECULAR CHARACTERIZATION OF A SARCOPLASMIC-ENDOPLASMIC RETICULUM CA-VAGINALIS(2 ATPASE GENE FROM TRICHOMONAS)

DNA fragments homologous to P-type cation translocating ATPase genes w ere identified in Trichomonas vaginalis by polymerase chain reaction ( PCR) amplification. The genomic locus corresponding to one PCR fragmen t, TVCA1, contains a 3,055 basepair open reading frame encoding a 108, 162 dalton protein composed of 981 amino acids, TVCA1 lacks introns, i s present in a single copy, and is expressed as a 3.1 kb transcript wi th short 5' and 3' untranslated regions. Separate primer extension exp eriments map the 5' end of the TVCA1 transcript to 12 and 16 nucleotid e bases (nti upstream of the methionine initiation codon. The message poly adenylation site is located 62 nt downstream of the protein termi nation codon at a CA dinucleotide. The TVCA1 protein sequence shares 5 7-58% similarity with rabbit, schistosome, trypanosome and malarial sa rcoplasmic-endoplasmic reticulum calcium (SERCA) pumps, and significan tly lower similarity with plasma membrane calcium pumps and cation tra nslocating ATPases of other ion specificities. Structural and function al domains identified in P-type ATPases as well as 61/68 residues spec ifically implicated in SERCA pump activity are conserved in TVCA1. How ever, TVCA1 lacks binding sites for phospholamban regulation, thapsiga rgin inhibition and the calmodulin dependent protein kinase site phosp horylation present in other SERCA pumps.