Tubular Mitochondria Research Articles

Mitochondrial complex I deficiency in GDAP1-related autosomal dominant Charcot-Marie-Tooth disease (CMT2K)

Mutations in GDAP1, an outer mitochondrial membrane protein responsible for recessive Charcot-Marie-Tooth disease (CMT4A), have also been associated with CMT2K, a dominant form of the disease. The three CMT2K patients we studied carried a novel dominant GDAP1 mutation, C240Y (c.719G > A). Mitochondrial respiratory chain complex I activity in fibroblasts from CMT2K patients was 40% lower than in controls, whereas the tubular mitochondria were 33% larger in diameter and the mitochondrial mass was 20% greater. Thus, besides the regulatory role GDAP1 plays in mitochondrial network dynamics, it may also be involved in energy production and in the control of mitochondrial volume.

Protein Trafficking insideToxoplasma gondii

The accurate targeting of proteins to their final destination is an essential process in all living cells. Apicomplexans are obligate intracellular protozoan parasites that possess a compartmental organization similar to that of free-living eukaryotes but can be viewed as professional secretory cells. Establishment of parasitism involves the sequential secretion from highly specialized secretory organelles, including micronemes, rhoptries and dense granules. Additionally, apicomplexans harbor a tubular mitochondrion, a nonphotosynthetic plastid organelle termed the apicoplast, acidocalcisomes and an elaborated inner membrane complex composed of flattened membrane cisternae that are derived from the secretory pathway. Given the multitude of destinations both inside and outside the parasite, the endoplasmic reticulum/Golgi of the apicomplexans constitutes one of the most busy roads intersections in eukaryotic traffic.

P166, a link between the trypanosome mitochondrial DNA and flagellum, mediates genome segregation

Kinetoplast DNA (kDNA), the trypanosome mitochondrial genome, is a giant network containing several thousand interlocked DNA rings. Within the mitochondrion, kDNA is condensed into a disk-shaped structure positioned near the flagellar basal body. The disk is linked to the basal body by a remarkable transmembrane filament system named the tripartite attachment complex (TAC). Following kDNA replication, the TAC mediates network segregation, pulling the progeny networks into the daughter cells by their linkage to the basal bodies. So far TAC has been characterized only morphologically with no known protein components. By screening an RNAi library, we discovered p166, a protein localizing between the kDNA and basal body in intact cells and in isolated flagellum-kDNA complexes. RNAi of p166 has only small effects on kDNA replication, but it causes profound defects in network segregation. For example, kDNA replication without segregation causes the networks to grow to enormous size. Thus, p166 is the first reported molecular component of the TAC, and its discovery will facilitate study of kDNA segregation machinery at the molecular level.

Spermatid Differentiation and Sperm Ultrastructure of the Granular Ark, Tegillarca granosa (Bivalvia: Arcidae)

This study describes spermatogenesis and sperm ultrastructure of the granular ark, Tegillarca granosa using light and electron microscopy. In the active spermatogenic season, the testis comprises many spermatogenic follicles that contain germ cells in different developmental stages. Primary spermatocytes in the pachytene stage are characterized by synaptonemal complexes. The early spermatids are characterized by the appearance of several Golgi bodies, increased karyoplasmic electron density, and tubular mitochondria. The mass of proacrosomal granules consists of numerous heterogeneous granules with high electron density that are about 20 nm in diameter. From the midstage of spermiogenesis, the well-developed mitochondria in the cytoplasm aggregate posterior to the nucleus and surround the proximal and distal centrioles. The proacrosomal granules condense and form a single acrosome with a thin envelope. During late spermiogenesis, the acrosome begins to elongate becoming conical. The sperm is approximately <TEX>$35.0{\mu}m$</TEX> long and consists of a head, midpiece, and tail. The head comprises a round nucleus and a conical acrosome. A micro fibrous axial rod is observed between the nucleus and acrosome. The midpiece has a calyx-like structure with five mitochondria, and the tail, which has the typical "9+2" microtubular system, originates from the distal centriole.

MARCH‐V is a novel mitofusin 2‐ and Drp1‐binding protein able to change mitochondrial morphology

Mitofusins and Drp1 are key components in mitochondrial membrane fusion and division, but the molecular mechanism underlying the regulation of their activities remains to be clarified. Here, we identified human membrane-associated RING-CH (MARCH)-V as a novel transmembrane protein of the mitochondrial outer membrane. Immunoprecipitation studies demonstrated that MARCH-V interacts with mitofusin 2 (MFN2) and ubiquitinated forms of Drp1. Overexpression of MARCH-V promoted the formation of long tubular mitochondria in a manner that depends on MFN2 activity. By contrast, mutations in the RING finger caused fragmentation of mitochondria. We also show that MARCH-V promotes ubiquitination of Drp1. These results indicate that MARCH-V has a crucial role in the control of mitochondrial morphology by regulating MFN2 and Drp1 activities.

The Mitochondrial Fission Regulator DRP3B Does Not Regulate Cell Death in Plants

Recent reports have described dramatic alterations in mitochondrial morphology during metazoan apoptosis. A dynamin-related protein (DRP) associated with mitochondrial outer membrane fission is known to be involved in the regulation of apoptosis. This study analysed the relationship between mitochondrial fission and regulation of plant cell death. Transgenic plants were generated possessing Arabidopsis DRP3B (K56A), the dominant-negative form of Arabidopsis DRP, mitochondrial-targeted green fluorescent protein and mouse Bax. Arabidopsis plants over-expressing DRP3B (K56A) exhibited long tubular mitochondria. In these plants, mitochondria appeared as a string-of-beads during cell death. This indicates that DRP3B (K56A) prevented mitochondrial fission during plant cell death. However, in contrast to results for mammalian cells and yeast, Bax-induced cell death was not inhibited in DRP3B (K56A)-expressing plant cells. Similarly, hydrogen peroxide-, menadione-, darkness- and salicylic acid-induced cell death was not inhibited by DRP3B (K56A) expression. These results indicate that the systems controlling cell death in animals and plants are not common in terms of mitochondrial fission.

Ni2+ induces changes in the morphology of vacuoles, mitochondria and microtubules in Paxillus involutus cells

Organelles of ectomycorrhizal fungi are known to respond to changes in the extracellular environment. The response of vacuoles, mitochondria and microtubules to short-term nickel (Ni2+) exposure were investigated in hyphal tip cells of a Paxillus involutus from a heavy metal-rich soil. Vacuoles, mitochondria and microtubules were labelled with Oregon Green 488 carboxylic acid diacetate, 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)) and anti-alpha-tubulin antibodies, respectively; hyphae were treated with NiSO4 in the range of 0-1 mmol l(-1) and examined microscopically. Untreated hyphal tip cells contained tubular vacuole and mitochondrial networks. Ni2+ caused loss of organelle tubularity and severe microtubule disruption that were exposure-time and concentration dependent. Fine tubular vacuoles thickened and eventually became spherical in some hyphae, tubular mitochondria fragmented and microtubules shortened and aggregated into patches in most hyphae. Tubular vacuoles reformed on NiSO4 removal and tubular mitochondria in the presence of NiSO4 suggesting cellular detoxification. These results demonstrate that Ni2+ induces changes in organelle and microtubule morphology. Recovery of tubular organelles to pretreatment morphology after Ni2+ exposure suggests cellular detoxification of the metal ion.

Disruption of Fusion Results in Mitochondrial Heterogeneity and Dysfunction

Mitochondria undergo continual cycles of fusion and fission, and the balance of these opposing processes regulates mitochondrial morphology. Paradoxically, cells invest many resources to maintain tubular mitochondrial morphology, when reducing both fusion and fission simultaneously achieves the same end. This observation suggests a requirement for mitochondrial fusion, beyond maintenance of organelle morphology. Here, we show that cells with targeted null mutations in Mfn1 or Mfn2 retained low levels of mitochondrial fusion and escaped major cellular dysfunction. Analysis of these mutant cells showed that both homotypic and heterotypic interactions of Mfns are capable of fusion. In contrast, cells lacking both Mfn1 and Mfn2 completely lacked mitochondrial fusion and showed severe cellular defects, including poor cell growth, widespread heterogeneity of mitochondrial membrane potential, and decreased cellular respiration. Disruption of OPA1 by RNAi also blocked all mitochondrial fusion and resulted in similar cellular defects. These defects in Mfn-null or OPA1-RNAi mammalian cells were corrected upon restoration of mitochondrial fusion, unlike the irreversible defects found in fzodelta yeast. In contrast, fragmentation of mitochondria, without severe loss of fusion, did not result in such cellular defects. Our results showed that key cellular functions decline as mitochondrial fusion is progressively abrogated.

Stage-specific expression of the mitochondrial co-chaperonin of Leishmania donovani, CPN10

BackgroundLeishmania spp., in the course of their parasitic life cycle, encounter two vastly different environments: the gut of sandflies and the phagosomes of mammalian macrophages. During transmission into a mammal, the parasites are exposed to increased ambient temperature as well as to different carbon sources. Molecular chaperones or heat shock proteins are implicated in the necessary adaptations which involve the ordered differentiation from the flagellated, extracellular promastigote to the intracellular amastigote stage.ResultsHere, we show that the Leishmania donovani co-chaperonin, CPN10, is synthesised to a significantly increased concentration during in vitro differentiation to the amastigote stage. We show by fluorescence microscopy and by immunogold electron microscopy that, like its putative complex partner CPN60.2, CPN10 is localised to the single, tubular mitochondrion of the parasites and, moreover, that it co-precipitates with CPN60.2, the major mitochondrial chaperonin of Leishmania spp..ConclusionOur data indicate an increased requirement for CPN10 in the context of mitochondrial protein folding during or early in the mammalian stage of this pathogen. Moreover, they confirm the CPN60.2 as bona fide mitochondrial GroEL homologue in L. donovani and the postulated interaction of eukaryotic chaperonins, CPN60 and CPN10.

Inhibition of mitochondrial bioenergetics: the effects on structure of mitochondria in the cell and on apoptosis.

The effects of specific inhibitors of respiratory chain, F(o)F(1)ATP synthase and uncouplers of oxidative phosphorylation on survival of carcinoma HeLa cells and on the structure of mitochondria in the cells were studied. The inhibitors of respiration (piericidin, antimycin, myxothiazol), the F(1)-component of ATP synthase (aurovertin) and uncouplers (DNP, FCCP) did not affect viability of HeLa cells, apoptosis induced by TNF or staurosporin and the anti-apoptotic action of Bcl-2. Apoptosis was induced by combined action of respiratory inhibitors and uncouplers indicating possible pro-apoptotic action of reactive oxygen species (ROS) generated by mitochondria. Short-term incubation of HeLa cells with the mitochondrial inhibitors and 2-deoxyglucose followed by 24-48 h recovery resulted in massive apoptosis. Apoptosis correlated to transient (3-4 h) and limited (60-70%) depletion of ATP. More prolonged or more complete transient ATP depletion induced pronounced necrosis. The inhibitors of respiration and uncouplers caused fragmentation of tubular mitochondria and formation of small round bodies followed by swelling. These transitions were not accompanied with release of cytochrome c into the cytosol and were fully reversible. The combined effect of respiratory inhibitors and uncouplers developed more rapidly indicating possible involvement of ROS generated by mitochondria. More prolonged (48-72 h) incubation with this combination of inhibitors caused clustering and degradation of mitochondria.

Effects of toltrazuril and ponazuril on the fine structure and multiplication of tachyzoites of the NC-1 strain of Neospora caninum (a synonym of Hammondia heydorni) in cell cultures.

Rhesus monkey kidney cell cultures were used to propagate tachyzoites of the NC-1 strain of Neospora caninum (syn. Hammondia heydorni). The infected cell cultures were incubated for 4-12 h in media containing 0, 1, 10 or 100 microg/ml of either toltrazuril or ponazuril. The effects were studied by light and electron microscopy. Drug dosages of at least 30 microg/ml were needed to eliminate the parasites. Ponazuril was found (with respect to the reduction of the number of parasites) to be less effective at dosages of 30 microg/ml compared to toltrazuril. However, the damage to the tachyzoites being incubated in 30 microg toltrazuril or ponazuril seen by electron microscopy was so significant that it was surely lethal. The initial damage occurred within the apicoplast and the tubular mitochondrion in all cases,thus destroying two of the most important cell organelles.

꼬막(Tegillarca granosa) 외투막의 미세구조

Histochemical characteristic and ultrastructure of the mantle of the granular ark, Tegillarca granosa are described using light and electron microscopy. The mantle of the clam is composed of outer epidermis, connective tissue and inner epidermis. The simple epidermis consists of supporting cells, ciliated cells of the two types and secretory cells of three types. Connective tissue is composed of matrix, collagen fibers, muscular fibers and hemolymph sinus. The columnar supporting cell is covered with microvilli on the free surface. Ciliated cells are distributed in the inner epidermis with numerous cilia, microvilli and tubular mitochondria. Secretory cells could be classified into three types (A, B and C) with morphological features of the secretory granules. Type A secretory cells contains secretory granules with fibrous materials of high electron density Type B secretory cells are more abundant than the other cells, and contains secretory granules of membrane-bounded and high electron density. Secretory granules of the type C cells are divided into fibrous core layer and homogeneous peripheral layer. Type B secretory cells are abundant in the both epidermis of marginal mantle, while large number of type A and C secretory cells are evident in the outer epidermis of the central and umbonal mantle. This result showed that the outer and the inner epidermis of the mantle are related with shell formation and cleaning of the mantle cavity, respectively.

Fine structure of erythrocytic stages of a Plasmodium tropiduri-like malaria parasite found in the lizard Kentropyx calcarata (Teiidae) from north Brazil.

The fine structure is described of the merogonic stages and gametocytes of a Plasmodium tropiduri Aragão et Neiva, 1909-like parasite infecting the teiid lizard Kentropyx calcarata Spix from North Brazil. The trophozoites are bordered by two membranes, and with growth a pellicle is formed by the addition of an inner, thick double layer and fragmented membrane. The same type of inner membrane occurs in the pellicle of the merozoites differentiating from the meronts. Merozoites contained a large electron-dense body, sometimes seen to be embraced by a tubular mitochondrion with a dense matrix. Micro- and macrogametocytes are bounded by a double membrane, closely apposed by the detached wall of the parasitophorous vacuole. Both contain osmiophilic bodies. The microgametocyte contains an electron-dense aggregate, and the macrogametocyte has a large mitochondrion and a complex of tubuli and cisternae. These features are compared with those described in other malarial parasites.

볼락 (Sebastes inermis) 난병 유사구조의 전자현미경적 기재

볼락의 난소는 낭상형이며, 다수의 난소소엽으로 구성되어 있었다. 난황축적 이전의 난모세포들은 난소소엽의 결체성 조직에 매몰되어 관찰되었다. 난모세포는 성장하면서 난소강으로 돌출되어 난병 유사구조를 가지고 포도송이와 같은 구조를 나타냈다 난소 소엽내에 매몰되어있는 직경 약 20<TEX>$\mu$</TEX>m 크기의 초기 난모세포에서 난황과립과 방사대는 관찰되지 않았다 직경 약 80<TEX>$\mu$</TEX>m의 초기 난모세포의 난병 유사구조 세포질에서는 전자밀도가 높은 난황과려들이 다수 관찰되었으나, 방사대의 pore canal system에서 음세포작용은 관찰되지 않았다. 이 시기에 난병 유사구조에서는 미세섬유, 발달된 소포체와 미토콘드리아, 전자밀도가 낮은 과립상 물질 그리고 활성화된 multivesicular body들이 관찰되었다. 이러한 결과들은 볼락의 난병 유사구조는 난모세포의 부착과 초기 난모세포의 외재적 난황축적에 관여함을 시사하는 것이라고 할 수 있다. The ovary of the rockfish, Sebastes inermis was cystovarian condition and consists of numerous ovarian lobules. Previtellogenic oocytes were embedded in the connective tissue of the ovarian lobules. As the oocytes grows, it protruded into the ovarian cavity and form grapes cluster-like structure with egg stalk-like structure. Yolk granules and zona radiata were not observed in the embedded early oocytes about 20 <TEX>$\mu$</TEX>m in diameter. In the oocytes about 80 <TEX>$\mu$</TEX>m in diameter, yolk granules with electron dense were abundant in the ooplasm near the egg stalk-like structure. However, pinocytosis was not obsened in the pore canal system of the zona radiata. In this stage, microfilaments, developed endoplasmic reticula, tubular mitochondria, granular materials with low electron density and active multivesicular bodies were observed in the egg stalk-like structure. This results suggest that the egg stalk-like structure of the rockfish are related with the oocyte attachment and exogenous vitellogenesis of the intial vitellogenic oocyte.

Molecular cloning, organellar targeting and developmental expression of mitochondrial chaperone HSP60 in Toxoplasma gondii

The obligate intracellular protozoan parasite Toxoplasma gondii has a single tubular mitochondrion. During infection, it recruits the host cell's mitochondria abutting to the intracellular vacuole, that contains the parasites. The respective contribution of host and parasitic mitochondria in the intracellular growth of T. gondii remains unknown. Heat shock protein, HSP60 has been reported in all eukaryotes examined, as an essential chaperone required for the folding and multimeric complex assembly of mitochondrial proteins. Here, we report the isolation and molecular characterization of two cDNAs corresponding to a single T. gondii gene coding for HSP60. Using a model fusion protein, preHSP60-chloramphenicol acetyl transferase (CAT), we demonstrate that the classical 22 amino acid mitochondrial presequence and the adjacent 32 amino acids of the mature protein are both required for the in vivo import into T. gondii mitochondria. The T. gondii HSP60 gene composed of five introns and six exons is transcribed into two related but differently spliced transcripts. Whereas the two transcripts can be detected in both developmental stages within the intermediate host, their levels are significantly increased in bradyzoites when compared to tachyzoites. By immunoblot analysis, the predicted 60-kDa protien corresponding to HSP60 was detected in both tachyzoite and bradyzoite forms. Using immunofluorescence assays, the polyclonal antibodies specific to T. gondii HSP60 recognized the mitochondrion in tachyzoites, as expected. In contrast, these antibodies reacted against two unknown vesicular bodies which are distinct from the classical mitochondrial pattern in bradyzoites. Taken together, these expression patterns of mitochondrial chaperone HSP60 suggests stage-specific induction of the respiratory pathway in the protozoan parasite T. gondii.

Ultrastructural features of non-commissural GABAergic neurons in the medial vestibular nucleus of the monkey

The ultrastructural characteristics of non-degenerating GABAergic neurons in rostrolateral medial vestibular nucleus were identified in monkeys following midline transection of vestibular commissural fibers. In the previous papers, we reported that most degenerated cells and terminals in this tissue were located in rostrolateral medial vestibular nucleus, and that many of these neurons were GABA-immunoreactive. In the present study, we examined the ultrastructural features of the remaining neuronal elements in this medial vestibular nucleus region, in order to identify and characterize the GABAergic cells that are not directly involved in the vestibular commissural pathway related to the velocity storage mechanism. Such cells are primarily small, with centrally-placed nuclei. Axosomatic synapses are concentrated on polar regions of the somata. The proximal dendrites of GABAergic cells are surrounded by boutons, although distal dendrites receive only occasional synaptic contacts. Two types of non-degenerated GABAergic boutons are distinguished. Type A terminals are large, with very densely-packed spherical synaptic vesicles and clusters of large, irregularly-shaped mitochondria with wide matrix spaces. Such boutons form symmetric synapses, primarily with small GABAergic and non-GABAergic dendrites. Type B terminals are smaller and contain a moderate density of round/pleomorphic vesicles, numerous small round or tubular mitochondria, cisterns and vacuoles. These boutons serve both pre- and postsynaptic roles in symmetric contacts with non-GABAergic axon terminals. On the basis of ultrastructural observations of immunostained tissue, we conclude that at least two types of GABAergic neurons are present in the rostrolateral portion of the monkey medial vestibular nucleus: neurons related to the velocity storage pathway, and a class of vestibular interneurons. A multiplicity of GABAergic bouton types are also observed, and categorized on the basis of subcellular morphology. We hypothesize that “Type A” boutons correspond to Purkinje cell afferents in rostrolateral medial vestibular nucleus, “Type B” terminals represent the axons of GABAergic medial vestibular nucleus interneurons, and “Type C” boutons take origin from vestibular commissural neurons of the velocity storage pathway.

Ultrastructure of vestibular commissural neurons related to velocity storage in the monkey

The angular vestibulo-ocular reflex maintains gaze during head movements. It is thought to be mediated by two components: direct and velocity storage pathways. The direct angular vestibulo-ocular reflex is conveyed by a three neuron chain from the labyrinth to the ocular motoneurons. The indirect pathway involves a more complex neural network that utilizes a portion of the vestibular commissure. The purpose of the present study was to identify the ultrastructural characteristics of commissural neurons in the medial vestibular nucleus that are related to the velocity storage component of the angular vestibulo-ocular reflex. Ultrastructural studies of degenerating medial vestibular nucleus neurons were conducted in monkeys following midline section of rostral medullary commissural fibers with subsequent behavioral testing. After this lesion, oculomotor and vestibular functions attributable to velocity storage were abolished, whereas the direct angular vestibulo-ocular reflex pathway remained intact. Since this damage was functionally discrete, degenerating neurons were interpreted as potential participants in the velocity storage network. Ultrastructural observations indicate that commissural neurons related to velocity storage are small and medium sized cells having large nuclei with deep indentations and relatively little cytoplasm, which are located in the lateral crescents of rostral medial vestibular nucleus. The morphology of degenerating dendritic profiles varied. Some contained numerous round or tubular mitochondria in a pale cytoplasmic matrix with few other organelles, while others had few mitochondria but many cisterns and vacuoles in dense granular cytoplasm. The commissural nature of these cells was further suggested by the presence of two different types of degenerating axon terminals in the rostral medial vestibular nucleus: those with a moderate density of large spherical synaptic vesicles, and those with pleomorphic, primarily ellipsoid synaptic vesicles. The recognition of two types of degenerating terminals further supports our interpretation that at least two morphological types of commissural neurons participate in the velocity storage network. The degenerating boutons formed contacts with a variety of postsynaptic partners. In particular, synapses were observed between degenerating boutons and non-degenerating dendrites, and between intact terminals and degenerating dendrites. However, degenerating pre- and postsynaptic elements were rarely observed in direct contact, suggesting that additional neurons are interposed in the indirect pathway commissural system. On the basis of these ultrastructural observations, it is concluded that vestibular commissural neurons involved in the mediation of velocity storage have distinguishing ultrastructural features and synaptology, that are different from those of direct pathway neurons.

Imidazole-induced morphological abnormalities of mitochondria of Candida albicans.

The mitochondrial morphology of live Candida albicans samples treated with several imidazoles (miconazole, econazole and clotrimazole) was observed with a fluorescent carbocyanine probe, 3,3'-dihexyloxacarbocyanine [diO-C6-(3)], under a fluorescence microscope. Nearly all non-treated C. albicans cells carried only long tubular mitochondria. Treatment with antimycotics at half the minimum inhibitory concentrations (MIC100) rapidly induced mitochondrial cleavage or fragmentation, which was followed by recovery to the normal tubular morphology within 1 h. Exposing the yeast to drugs at concentrations higher than the MICs resulted in the development of swollen mitochondria or amorphous bodies. These phenomena were concentration dependent. The fluorescence images were also compared with ultrastructural images obtained by transmission electron microscopy.

Encystment and excystment of a trypanosomatid of the genus Leptomonas

Summary Morphological events leading to cyst formation in a cyst-bearing Leptomonas sp. isolated from the hemipteran Oncopeltus varicolor were monitored by light and electron microscopy. In LIT cultures, cyst-bearing flagellates appear at the end of the lag phase and from then on the number of detached mature cysts increases steadily. The cysts develop at the point of the flagellum-cell body junction from the parental flagellate. Plasma-membranes of flagellate and cysts remain connected while they remain attached. Immature cysts present microtubules and a large tubular mitochondrion. Mature cysts are dense, ovalshaped, with few distinguishable organelles, such as a modified nucleus, a rudimentary flagellar pocket and a network of fibrils possibly of kinetoplast origin. During excystation, cysts gradually regain the missing organelles and morphological features of active promasti-gotes. Even cysts, with a very dense and distinct chromatin, retain the ability to undergo cell division in culture.

Characterization of two nuclear-encoded protein components of mitochondrial ribonucleoprotein complexes from Leishmania tarentolae

Two mitochondrial proteins with molecular masses of 18 and 51 kDa were isolated from Leishmania tarentolae, and N-terminal amino-acid sequences were obtained. The cDNAs and genes encoding these proteins were cloned using RT-PCR. The proteins were identified as components of the previously characterized mitochondrial ribonucleoprotein complexes, T-Ia and T-VI, by comigration in native gels. The p18 and p51 genes contain 17 and 9-amino-acid N-terminal sequences, which are not present in the mature proteins and may represent cleavable mitochondrial targeting sequences. There are two identical p18 genes separated by 1.7 kb in tandem array and both are transcribed. The p18 amino-acid sequence is not similar to any sequence in the database. Antiserum to p18 expressed in Escherichia coli reacts with the entire tubular mitochondrion. The p51 gene is single copy, and the amino-acid sequence is similar to mitochondrial aldehyde dehydrogenases from other organisms. The N-terminal amino-acid sequences of 71 and 62-kDa mitochondrial proteins which co-migrated in native gels with several other T-complexes were also obtained. The p71 sequence proved to be similar to hsp70 sequences from other organisms. The p62 sequence was identical to an hsp60 sequence from Trypanosoma brucei.