Antibodies against Tetrahymena 14-nm filament-forming protein recognize the replication band in Euplotes

Identification of Tetrahymena hsp60 as a 14-nm filament protein/citrate synthase-binding protein and its possible involvement in the oral apparatus formation

BACKGROUND

Tetrahymena 14-nm filament protein (14FP) is bifunctional, with roles as a citrate synthase in mitochondria and as a cytoskeletal protein in nuclear events during fertilization and in oral morphogenesis. In this study, to further our understanding of the bifunctional property of 14FP, we attempted to screen 14FP-binding proteins using affinity column chromatography.

RESULTS

Through the screening of 14FP-binding proteins using 14FP-affinity chromatography, we detected 65 kDa and 70 kDa proteins that bound to 14FP in an ATP dependent manner. From the N-terminal amino acid sequence, these proteins were identified as the Tetrahymena mitochondrial chaperones, hsp60 and mthsp70, respectively. Tetrahymena hsp60 was recognized with a monoclonal antibody raised against human hsp60. Immunofluorescence and immunoelectron microscopy using the monoclonal antibody showed that Tetrahymena hsp60 was localized to mitochondria. Moreover, Tetrahymena hsp60 was also present at extramitochondrial sites including basal bodies of cilia and oral apparatus, and particularly at the developing oral apparatus during cell division.

CONCLUSION

These results suggest that Tetrahymena hsp60 is localized in basal bodies and is involved in cortical patterning such as the formation of the oral apparatus as well as having a role in the folding of mitochondrial proteins in mitochondria.

Direct demonstration of the bifunctional property of Tetrahymena 14-nm filament protein/citrate synthase following expression of the gene in Escherichia coli

Tetrahymena 14-nm filament protein/citrate synthase (49K protein) is a bifunctional protein with roles in the cytoskeleton and as a citrate synthase. Though previous studies have shown that the 49K protein is derived from a single transcript of a single gene, direct demonstration of the 49K protein's bifunctional property remained to be elucidated. In this study, a recombinant 49K protein was expressed in Escherichia coli, purified and characterized. The citrate synthase activity of the recombinant 49K protein was comparable to that of the 49K protein purified from Tetrahymena. The recombinant 49K protein formed 14-nm filaments, but only of short length. The filaments were elongated in the presence of a soluble fraction of Tetrahymena. These results suggest that the 49K protein itself is bifunctional, but some co-factor(s) is necessary for elongation of filaments.

Multifunctional proteins in Tetrahymena: 14-nm filament protein/citrate synthase and translation elongation factor-1 alpha

One gene encoding a protein has been shown to have two entirely different functions. Such a phenomenon, which has been called "gene sharing," was first known in crystallins. We found two multifunctional proteins in the ciliated protozoan Tetrahymena: 14-nm filament protein and protein translation elongation factor 1-alpha (EF-1 alpha). The 14-nm filament protein has dual functions as a citrate synthase in mitochondria and as a cytoskeletal protein in cytoplasm. In cytoplasm, the 14-nm filament protein was involved in oral morphogenesis and in pronuclear behavior during conjugation. The observation that Tetrahymena intramitochondrial filamentous inclusions contain the 14-nm filament protein and that the citrate synthase activity of the 14-nm filament protein is decreased by polymerization and increased by depolymerization, suggests a possible modulating mechanism of citrate synthase activity by monomer-polymer conversion in mitochondria in situ. The EF-1 alpha functions as an F-actin-bundling protein and a 14-nm filament-associated protein as well as an elongation factor in protein synthesis. The F-actin-bundling activity of EF-1 alpha was regulated by Ca2+ and calmodulin. Here we review the properties and functions of two multifunctional proteins in Tetrahymena.

The DNA of ciliated protozoa

Ciliates contain two types of nuclei: a micronucleus and a macronucleus. The micronucleus serves as the germ line nucleus but does not express its genes. The macronucleus provides the nuclear RNA for vegetative growth. Mating cells exchange haploid micronuclei, and a new macronucleus develops from a new diploid micronucleus. The old macronucleus is destroyed. This conversion consists of amplification, elimination, fragmentation, and splicing of DNA sequences on a massive scale. Fragmentation produces subchromosomal molecules in Tetrahymena and Paramecium cells and much smaller, gene-sized molecules in hypotrichous ciliates to which telomere sequences are added. These molecules are then amplified, some to higher copy numbers than others. rDNA is differentially amplified to thousands of copies per macronucleus. Eliminated sequences include transposonlike elements and sequences called internal eliminated sequences that interrupt gene coding regions in the micronuclear genome. Some, perhaps all, of these are excised as circular molecules and destroyed. In at least some hypotrichs, segments of some micronuclear genes are scrambled in a nonfunctional order and are recorded during macronuclear development. Vegetatively growing ciliates appear to possess a mechanism for adjusting copy numbers of individual genes, which corrects gene imbalances resulting from random distribution of DNA molecules during amitosis of the macronucleus. Other distinctive features of ciliate DNA include an altered use of the conventional stop codons.

Identification of the epiplasmins, a new set of cortical proteins of the membrane cytoskeleton in Paramecium

In most ciliates, the epiplasm, a superficial cytoskeletal layer of variable thickness, both surrounds basal bodies and interacts tightly with adjacent membrane networks; it constitutes the predominant structure in Paramecium cell ghosts. Previous indirect data suggested several cortical proteins as potential constituents of the epiplasm. New sharp monoclonal antibodies presented in this paper, positive both on immunotransfers and in immunocytochemical tests carried out on permeabilized cells and ultrathin sections, definitively identify the epiplasmins: a set of about twenty protein bands ranging from 45 to 33 kDa and making up the bulk of the epiplasmic layer. The complete epiplasmin pattern characterized from gradient-purified cortex is also present in unfractionated whole cells, confirming that the pattern is not generated artifactually. Comparative one-step extractions, performed either in 1 M KI or in 4 M urea, solubilize the epiplasmins as a whole, indicating that all of them share very similar biochemical properties. Two-dimensional electrophoresis shows the great complexity of this epiplasmin group. Epiplasmin solubilization properties are discussed with respect to other models of membrane-cytoskeleton interaction developed among protists and metazoans and also to intermediate filaments, specially lamins. Immunofluorescent labelling combined with confocal microscopy permits a more detailed study of epiplasm formation at the level of the fission furrow, with new insights into two successive steps of epiplasm growth. A first series of interspecific reactions has been carried out with one of the anti- epiplasmin antibodies, yielding results which are discussed in an evolutionary framework.

Identification of Tetrahymena 14-nm filament-associated protein as elongation factor 1 alpha

Tetrahymena 14-nm filament-forming protein has dual functions as a citrate synthase in mitochondria and as a cytoskeletal protein involved in oral morphogenesis and in pronuclear behavior during conjugation. By immunoblotting using monoclonal and polyclonal antibodies following two-dimensional gel electrophoresis, we demonstrated that the 14-nm filament protein fraction contained two 49-kDa proteins whose isoelectric points were 8.0 and 9.0; a monoclonal antibody (MAb) 26B4 and a polyclonal antibody 49KI reacted only to a pI 8.0 protein, while two other MAbs, 11B6 and 11B8, reacted only to a pI 9.0 protein. From the N-terminal amino acid sequences, the pI 8.0 protein was identified as the previously reported 14-nm filament-forming protein/citrate synthase, but the pI 9.0 protein N-terminal sequence had no similarity with that of the pI 8.0 protein. The pI 9.0 protein is considered to be a 14-nm filament-associated protein since the pI 9.0 protein copurifies with the pI 8.0 protein during two cycles of an assembly and disassembly purification protocol. Cloning and sequencing the pI 9.0 protein gene from a Tetrahymena pyriformis cDNA library, we identified the pI 9.0 protein as elongation factor 1 alpha (EF-1 alpha) based on it sharing 73-76% sequence identity with EF-1 alpha from several species.