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Folia Biol (Krakow). 2015;63(3):195-213.

The ts111 Mutation of Paramecium tetraurelia Affects a Member of the Protein Palmitoylation Family.


The thermosensitive ts111 mutant of Parameciun tetraurelia carries a recessive mutation which causes cell death after 2-8 divisions at the restrictive temperature of 35 degrees C. Expression at 35 degrees C induces disassembly of the infraciliary lattice (ICL). In this study, we found that the ts111 mutation also results in significant abnormalities in the number and structure of contractile vacuole complexes (CVCs) and in their functioning at the restrictive temperature. In order to characterize the ts111 gene, the complementation cloning was performed by microinjection into the macronucleus of an indexed genomic DNA library. The mutation was complemented by a sequence of 852 bp, which differed from the mutant sequence by a single nucleotide substitution. The deduced protein sequence is 284 amino acids long. It contains a domain referred to as the DHHC domain, associated with 2 trans-membrane helices. The DHHC proteins belong to the Palmitoyl-Acyl Transferases (PATs) protein family, which is implicated in the protein palmitoylation process playing the role in protein addressing. The ts111 mutation induces the amino acid change, localized before the first membrane helix. Transformation of ts111 mutant cells with the TS111-GFP gene fusion showed the expected reparation restoring thermoresistance and also demonstrated a localization of the protein in contractile vacuoles, but not in the ICL. The entire gene silencing in wild type cells at restrictive temperature caused the same effect as the expression of a point mutation in ts111 mutant. The authors propose the following hypotheses: (i) function of CVCs at the restrictive temperature depends in Paramecium on the TS111 protein--a member of the PAT family, and the primary effect of the termosensitive ts111 mutation are morphological abnormalities and dysfunction of CVCs, (ii) disassembly of the ICL is a secondary effect of the ts111 mutation, which results from disturbed regulation of the intracellular concentration of Ca(+2) ions caused by the abnormal functioning of CVC.

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