Linked genes for calmodulin and E2 ubiquitin-conjugating enzyme in Trichomonas vaginalis

Separable putative polyadenylation and cleavage motifs in Trichomonas vaginalis mRNAs

3' Untranslated region processing and polyadenylation in Trichomonas vaginalis was analyzed by 3' rapid amplification of cDNA ends and sequence analysis of T. vaginalis mRNAs. A putative polyadenylation signal with the sequence UAAA was found 11-30 nucleotides upstream from the cleavage site. The motif pyrimidine( downward arrow)(A)(0-3)AAUU is proposed to be the cleavage site for polyadenylation of transcripts. This potential sequence defining the cleavage site for polyadenylation in eukaryotes is a novel finding. As in other eukaryotes, runs of several U's downstream from the cleavage site were identified. A working hypothesis is proposed which couples the UAA translation stop codon with the signaling for the 3'end processing of transcripts in this early divergent parasitic protozoa.

A homologue of CROC-1 in a ciliated protist (Sterkiella histriomuscorum) testifies to the ancient origin of the ubiquitin-conjugating enzyme variant family

Resting cysts of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) have been shown to contain messenger RNA, one of which codes for a protein significantly similar to CROC-1. CROC-1 is a human regulatory protein capable of transactivating the promoter of c-fos and belongs to a newly characterized family of ubiquitin-conjugating enzyme (E2) variants (UEV). We have determined the corresponding macronuclear gene sequence, which is the first protistan UEV sequence available. The phylogenetic analysis indicates the deep separation and solid clustering of all the UEV sequences within the E2 tree showing the ancient origin of these regulatory genes and their high structural conservation during evolution. Furthermore, overexpression of the ciliate UEV is able to rescue the Saccharomyces cerevisiae mms2 null mutant from killing by DNA damaging agents, implying that the UEV family proteins are functionally conserved. In S. histriomuscorum, expression of UEV is correlated with the growth of the cells as transcripts are present in excysting and vegetative cells but are rapidly down-regulated during starvation. These data support the high conservation of the UEV family in eukaryotes, and a regulatory role of the gene is discussed in relation to known functions of UEVs. This analysis may promote the search for homologues of other regulatory genes (metazoan regulators of differentiation) in ciliates.

Differences between coding and non-coding regions in the Trichomonas vaginalis genome: an actin gene as a locus model(1)

The sequence of a cloned genomic fragment of Trichomonas vaginalis containing a complete actin gene was determined. An uninterrupted open reading frame of 1128 nucleotides was found that codes for an actin gene. Two overlapped consensus promoter sequences for T. vaginalis were found 12 nucleotides upstream the actin initiation codon. In addition to actin, two incomplete open reading frames were found at the 5' and 3' ends of the clone. These two sequences are expressed and showed similarity to adenylate cyclase genes and a yeast hypothetical protein. The overall sequence showed a higher G+C content and a lower frequency of repeated sequences in the coding regions when compared with the non-coding regions. A similar unequal nucleotide distribution was found in various T. vaginalis genes retrieved from data bases.

Reconstructing Early Events in Eukaryotic Evolution

Resolving the order of events that occurred during the transition from prokaryotic to eukaryotic cells remains one of the greatest problems in cell evolution. One view, the Archezoa hypothesis, proposes that the endosymbiotic origin of mitochondria occurred relatively late in eukaryotic evolution and that several mitochondrion-lacking protist groups diverged before the establishment of the organelle. Phylogenies based on small subunit ribosomal RNA and several protein-coding genes supported this proposal, placing amitochondriate protists such as diplomonads, parabasalids, and Microsporidia as the earliest diverging eukaryotic lineages. However, trees of other molecules, such as tubulins, heat shock protein 70, TATA box-binding protein, and the largest subunit of RNA polymerase II, indicate that Microsporidia are not deeply branching eukaryotes but instead are close relatives of the Fungi. Furthermore, recent discoveries of mitochondrion-derived genes in the nuclear genomes of entamoebae, Microsporidia, parabasalids, and diplomonads suggest that these organisms likely descend from mitochondrion-bearing ancestors. Although several protist lineages formally remain as candidates for Archezoa, most evidence suggests that the mitochondrial endosymbiosis took place prior to the divergence of all extant eukaryotes. In addition, discoveries of proteobacterial-like nuclear genes coding for cytoplasmic proteins indicate that the mitochondrial symbiont may have contributed more to the eukaryotic lineage than previously thought. As genome sequence data from parabasalids and diplomonads accumulate, it is becoming clear that the last common ancestor of these protist taxa and other extant eukaryotic groups already possessed many of the complex features found in most eukaryotes but lacking in prokaryotes. However, our confidence in the deeply branching position of diplomonads and parabasalids among eukaryotes is weakened by conflicting phylogenies and potential sources of artifact. Our current picture of early eukaryotic evolution is in a state of flux.

Cloning and molecular characterization of a cDNA clone coding for Trichomonas vaginalis alpha-actinin and intracellular localization of the protein

We have identified and sequenced a cDNA clone coding for Trichomonas vaginalis alpha-actinin. Analysis of the obtained sequence revealed that the 2,857-nucleotide-long cDNA contained an open reading frame encoding 849 amino acids which showed consistent homology with alpha-actinins of different species. Such homology was particularly significant in regions which have been reported to represent the actin-binding and Ca2+-binding domains in other alpha-actinins. The deduced protein was also characterized by the presence of a divergent central region thought to play a role in its high immunogenicity. A study of protein localization performed by immunofluorescence revealed that the protein is diffusely distributed throughout the T. vaginalis cytoplasm when the cell is pear shaped. When parasites adhere and transform into the amoeboid morphology, the protein is located only in areas close to the cytoplasmic membrane and colocalizes with actin. Concomitantly with transformation into the amoeboid morphology, alpha-actinin mRNA expression is upregulated.