Paternal cytoplasmic transmission in Chinese pine (Pinus tabulaeformis)

Summary. In this paper, the stages of normal sexual reproduction between pollen tube penetration of the archegonium and early embryo formation in Pinus tabulaeformis are described, emphasizing the transmission of parental cytoplasm, especially the DNA-containing organelles – plastids and mitochondria. The pollen tube growing in the nucellus contained an irregular tube nucleus followed by a pair of sperm cells. The tube cytoplasm contained abundant organelles, including starch-containing plastids and mitochondria. The two sperm cells differed in their volume of cytoplasm. The leading sperm, with more cytoplasm, contained abundant plastids and mitochondria, while the trailing one, with a thin layer of cytoplasm, had very few organelles. The mature egg cell contained a great number of mitochondria, whereas it lacked normal plastids. At fertilization, the pollen tube penetrated into the egg cell at the micropylar end and released all of its contents, including the two sperms. One of the sperm nuclei fused with the egg nucleus, whereas the other one was retained by the receptive vacuole. Very few plastids and mitochondria of male origin were observed around the fusing sperm and egg nuclei, while the retained sperm nucleus was surrounded by a large amount of male cytoplasm. The discharged tube cytoplasm occupied a large micropylar area in the egg cell. In the free nuclear proembryo, organelles of maternal and paternal origins intermingled in the neocytoplasm around the free nuclei. Most of the mitochondria had the same features as those of the egg cell, but some appeared to be from sperm cells and tube cytoplasm. Plastids were obviously of male origin, with an appearance similar to those of the sperm or tube cells. After cellularization of the proembryo, maternal mitochondria became more abundant than the paternal ones and the plastids enlarged and began to accumulate starch. The results reveal the cytological mechanism for paternal inheritance of plastids and biparental inheritance of mitochondria in Chinese pine. Correspondence and reprints: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Science, China Agricultural University, Beijing 100094, People’s Republic of China.     

Superoxide dismutase of plant cell vacuoles

Metal-dependent superoxide dismutases (SOD; EC 1.15.1.1) are present in many cell compartments (mitochondria, plastids, nuclei, peroxisomes, endoplasmic reticulum, cell wall and cytosol). We have established that SOD is also localized in the central vacuole. Cyanide-sensitive Cu, Zn-SOD was found in the fraction of isolated vacuoles of red beet roots (Beta vulgaris L.). The enzyme was represented by three isoforms. Comparison of isoenzyme composition and the level of SOD activity in vacuoles, nuclei, plastids and mitochondria isolated from root cells has shown that Cu, Zn-SOD is present in vacuoles and nuclei, two SOD forms (Cu, Zn- and Fe-SOD) are present in plastids, and two SOD forms (Cu, Zn- and Mn-SOD) are present in mitochondria. Cu, Zn-SOD of organelles, unlike vacuolar Cu, Zn-SOD, had only one isoform. The level of enzyme activity from the vacuolar fraction was twice higher than the level of SOD activity from the fractions of isolated organelles. Previously it has been suggested that Cu, Zn-SOD may be localized on the vacuolar membrane or in the near-membrane space from the side of cytoplasm. Our tests have revealed the Cu, Zn-SOD activity in water-soluble extracts of isolated vacuole fractions in the absence of detergent, which may confirm localization of the enzyme inside the organelles.     

The Endoplasmic Reticulum-Resident Chaperone Heat Shock Protein 47 Protects the Golgi Apparatus from the Effects of O-Glycosylation Inhibition

The Golgi apparatus is important for the transport of secretory cargo. Glycosylation is a major post-translational event. Recognition of O-glycans on proteins is necessary for glycoprotein trafficking. In this study, specific inhibition of O-glycosylation (Golgi stress) induced the expression of endoplasmic reticulum (ER)-resident heat shock protein (HSP) 47 in NIH3T3 cells, although cell death was not induced by Golgi stress alone. When HSP47 expression was downregulated by siRNA, inhibition of O-glycosylation caused cell death. Three days after the induction of Golgi stress, the Golgi apparatus was disassembled, many vacuoles appeared near the Golgi apparatus and extended into the cytoplasm, the nuclei had split, and cell death assay-positive cells appeared. Six hours after the induction of Golgi stress, HSP47-knockdown cells exhibited increased cleavage of Golgi-resident caspase-2. Furthermore, activation of mitochondrial caspase-9 and ER-resident unfolded protein response (UPR)-related molecules and efflux of cytochrome c from the mitochondria to the cytoplasm was observed in HSP47-knockdown cells 24 h after the induction of Golgi stress. These findings indicate that (i) the ER-resident chaperon HSP47 protected cells from Golgi stress, and (ii) Golgi stress-induced cell death caused by the inhibition of HSP47 expression resulted from caspase-2 activation in the Golgi apparatus, extending to the ER and mitochondria.     

Anatomical and ultrastructural study of the secretory cavity development ofCitrus sinensis and Citrus limon: evaluation of schizolysigenous ontogeny

The ontogeny and ultrastructure of secretory oil glands in the fruits of Citrus sinensis and Citrus limon were studied with light and electron microscopy (TEM). Oil glands were initiated by cell division in globular/oval clusters of young meristematic cells under or including also the epidermis. Successively, the central oil cells increased greatly in size by growth and coalescence of one or more vacuoles. Starting from these cells the oil cavity formation and enlargment occurred by schizogenous and lysigenous precesses which overlap one another. The separation of the cell walls, in both Citrus species, was accompanied by strong structural disorganization of the cytoplasm, loss of nuclei, plasmolysis, and followed by autolysis processes. Prior these changes a great quantity of oil droplets filled the cells. In Citrus sinensis this material was formed in the plastids; on the contrary, in Citrus limon oil droplets appeared only in the cytoplasm, and no connection with the plastids was observed. The processes of schizogeny and lysigeny occurred in a centrifugal direction. The peripheral oil chamber cells were so pushed outward and flattened with the progressive expansion of the gland cavity. Also these cells became vacuolated, showed schizogenous processes together with cytoplasm and nuclei breakdown. These cell modifications were preceded by an abundant essential oil synthesis. Electron dense material appeared in the cavity near the boundary cells. Among the cell layers surrounding the cavity, the outer peripheral cells showed very thick walls. These cells, probably, had a protective function, while the inner cells continued, at least in part, to produce and secrete oil compounds. In the two Citrus species the pattern of oil gland development was practically the same, except the different plastid behaviour.     

Ultrastructural study of the effect of TNT on callus cells and cells of intact plants of Yucca gloriosa L.

Intracellular distribution of assimilated 2,4,6-trinitrotoluene (TNT) in callus cells, flower buds, and leaves of intact Yucca gloriosa L. plants with the use of electron microscopy radioautography was carried out. The radiotracer was detected in vacuoles, plastids, mitochondria, endoplasmic reticulum, and cytoplasm. It was found that TNT incorporation in the vacuoles of dedifferentiated callus cells was higher compared to cells from intact plant. Therefore, the ultrastructural continuity of differentiated cells is less damaged.     

Mitochondrial deformation and apocrine secretory mechanism in the rabbit submandibular organ as revealed by electron microscopy

Summary The submandibular organ (a sort of apocrine sweat glands) of the rabbit was observed with the electron microscope. The cell structure of glandular tubules varies depending upon the secretory activity; there are three functional stages. The secretory cells at the resting stage are characterized by low height, absence of secretory substance, and presence of small and slender mitochondria.In the synthesizing stage, enlargement and peculiar deformation of mitochondria are observed. Secretory substance always occurs near the deformed mitochondria. The part of a mitochondrion closely abutting on the secretion mass is extremely thin, and contains longitudinally oriented cristae. Sometimes a direct continuity is observed between the thinned portion of the deformed mitochondria and the mass of secretory substance. It is presumed that the secretion is initially produced in the mitochondria and then discharged from them. The Golgi apparatus and the rough surfaced endoplasmic reticulum may be involved indirectly. Smooth surfaced vesicles, probably related to the transport of raw material, are extremely abundant in the cells of this stage.The development of a generally homogeneous projection into the gland lumen is characteristic of the stage of secretion discharge. The mitochondria are again small and slender, and the secretion is liquefied. At the base of the full-grown projection, cytoplasm is condensed to form a demarcation zone from which the projection may become detached. This mechanism of release of secretory product is quite the same as the so-called apocrine secretory process long postulated by light microscopists.     

The effect of calcium antagonists and inhibitors of secretory processes on auxin-induced elongation and fine structure ofPisum sativum stem segments

Summary The treatment of dark grown pea stem segments with chelators of divalent cations (EGTA, EDTA, CTC), various Ca²⁺ antagonists (LaCl₃, A-23187, verapamil) and inhibitors of secretory processes (monensin, CB) reduced elongation in the presence of indole-3-acetic acid (IAA). Generally the inhibition increased with increasing concentrations of the substances. The timing of the responses can be correlated with maximum auxin-stimulated secretion of cell wall material. Examination of cell ultrastructure showed that changes in dictyosome activity could explain a reduced deposition of cell wall material and so cause inhibition of elongation.The inhibitors affected the morphology and vesiculation of the dictyosomes, and the appearance of the plasma membrane, ER and mitochondria in different ways. The most pronounced effects on ultrastructure resulted from monensin and LaCl₃ treatments with the dictyosomes being most affected; large vesicles appeared in the cytoplasm. Less pronounced effects on cell structure were seen in EGTA, A-23187 and verapamil treated tissue. The effects on the dictyosomes are considered to be due to disturbances of Ca²⁺ and other ionic levels within the cells.Abbreviations ATPase adenosine triphosphatase - CB cytochalasin B - CTC chlorotetracycline - DMSO dimethyl sulphoxide - EDTA ethylene diamine tetraacetic acid - EGTA ethyleneglycol-bis-(B-amino ethyl ether)N,N¹-tetraacetic acid - ER endoplasmic reticulum - ver verapamil     

Ultrastructure and cytochemistry of the pearl gland in Piper regnellii (Piperaceae)

Pearl glands are scattered throughout the lamina of developing leaves and rarely found on adult leaves of Piper regnellii (Piperaceae). The pearl gland is a bicellular secretory trichome composed of a short broad basal cell and a spatula-like, semiglobular apical cell. Four different stages of the pearl gland were determined during its ontogenesis: origin, pre-secretory, secretory and post-secretory. During the pre-secretory stage, mitochondria, ribosomes, dictyosomes, rough endoplasmic reticulum, and plastids with electron dense inclusions were present in the cytoplasm of the apical cell. During the secretory stage, the most remarkable characteristics of the apical cell are the proliferation of dictyosomes and their vesicles, rough endoplasmic reticulum, and modified plastids. At this stage, electron-dense oil drops occur in the plastids as well as scattered within the cytoplasm, proteins and polysaccharides are seen in the plastids, vesicles, and vacuoles. Only polysaccharides are present in the periplasmic space, wall cavities, and on the surface of the apical cell. The polysaccharides are one of the main components of the mucilagenous exudate that covers the developing leaf structures. The apical cell of the senescing trichomes undergoes a progressive degeneration of its cellular components, the plastids being the first organelles to undergo lysis.     

Ultrastructural Studies of Microsporogenesis in Phaseolus vulgaris L.

Microsporogenesis in dwarf Phaseolus vulgaris was studied under the electron microscope. Before meiosis the microspore mother cell had a lot of organelles especially plastids and ER in its cytoplasm. There were many osmiophilic granules adhering to the membranes of the plastids and vesicular ER until meiosis began. Some cytoplasmic channels were present between adjacent microsporocytes from pachytene to telophase Ⅱ. The organelles were at early stage in the early rnlcrospore, the plastids and mitochondria of which showed regional distribution. Original vacou[es were produced by smooth ER. The organelles in the tapetum cells were mainly mitochondria, plastids and ER. The ER was concentric circles in shape in transverse section.     

Anatomy and ultrastructure of the floral nectary in Peganum harmala L. (Nitrariaceae)

Anatomy and ultrastructure of the floral nectary of Peganum harmala L. were studied using light and transmission electron microscopy. The floral nectary was visible as a glabrous, regularly five‐lobed circular disc encircling the base of the ovary. Anatomically, it comprised a single layered epidermis and 15–20 layers of small, subepidermal secretory cells overlying several layers of large, ground parenchyma cells. The floral nectary was supplied by phloem and both sieve tubes and companion cells were found adjacent to the ground parenchyma. Based on our ultrastructural observations, plastids of secretory cells during the early stages of development were rich in starch grains and/or osmiophilic plastoglobuli, but these disappeared as nectar secretion progressed. The nectar appeared to exude through the modified stomata along symplastic and apoplastic routes. The abundant plastids and mitochondria suggest an eccrine mechanism of nectar secretion in P. harmala.     

Seasonal changes in the structure and secretory activity of the androgenic gland of Travancoriana schirnerae

This study investigated the seasonal variation in the structure and secretory activity of the androgenic gland (AG) in the freshwater crab: Travancoriana schirnerae. The androgenic gland is an elongate structure, attached to one side on the wall of the ejaculatory duct. Histological studies showed the presence of three cell types, which differ in size, shape of nuclei, and presence or absence of secretory vesicles. Type I cells are small with large nuclei whereas type II cells are large with small nuclei. Type III cells are intermediate in size and exhibited streak-like nuclei and transparent cytoplasm. Seasonal changes were discerned in the morphology, histology and secretory activity of the gland. March-June appeared to be the active season with type II cells containing secretory vesicles. The mode of release of secretion found to be holocrine. The secretory activity almost completed by July-August (the mating season) with vacuolization of type II cells. The gland remained inactive from September-December with abundance of vacuoles, scattered pycnotic nuclei, indistinct cell membranes and total cellular degeneration. January-February was the revival period with type I cell proliferation. The present study revealed that the secretory activity of the gland is in tune with the male reproductive cycle.     

Ultrastructural specialization for ureide production in uninfected cells of soybean root nodules

Summary Ultrastructural studies were conducted on root nodules of soybean (Glycine max) inoculated as seeds withRhizobium japonicum. The development of the large peroxisomes and abundant tubular endoplasmic reticulum (ER) characteristic of the uninfected interstitial cells was followed during nodule growth and maturation. Quantitative data on differences between the uninfected and infected cells in volumes and numbers of peroxisomes, plastids and mitochondria were analyzed statistically. The peroxisomes are 60 times greater in volume per unit cytoplasm in the uninfected cells than the small presumptive peroxisomes in the infected cells. Plastids are about equal in volume in the two types of cells. Mitochondria have 4 × the volume and 3 × the number of profiles per unit cytoplasm in the infected cells than in the uninfected. The observations are discussed in relation to published evidence that several enzymes involved in ureide production are localized in organelles of the uninfected cells. The uninfected cells are viewed as essential components in the symbiotic relationship between host and bacterium.Abbreviations DAB 3,3-diaminobenzidine - ER endoplasmic reticulum     

Developmental Aspects of Ultrastructure, Histochemistry and Receptivity of the Stigma of Nicotiana sylvestris

The bilobed papillate stigma of Nicotiana sylvestris Speg. andComes, is covered at maturity with a copious exudate containinglipid, protein and carbohydrate. The stigma is receptive fromthe very early stage of development and it also stains positivelyfor esterase activity. The stigma has three distinct zones:an epidermis with papillae; a subepidermal secretory zone; anda parenchymatous ground tissue. The behaviour of the cells ofthese three zones has been followed from 6 d before anthesisto one day after anthesis and pollination. The cells of theepidermis and the secretory zone stain intensively for lipids,proteins and carbohydrates in the initial stages. The secretoryzone develops large intercellular spaces containing heterogenoussecretory products which also stain positively for the aforesaidthree compounds. At maturity the secretory products are releasedto the surface through gaps formed in the epidermis by cellseparation. The main secretion of the stigma is produced bythe cells of the secretory zone. Less secretion is derived fromthe stigmatic papillae. Some amount of secretion is also releasedfrom the stylar transmitting tissue adjoining the stigma. Theglandular cells of the stigma contain numerous plastids, mitochondria,ribosomes, ER, cytoplasmic lipid droplets and some dictyosomes.The plastids and the vacuoles in the secretory cells of thestigma have a lot of electron dense (osmiophilic) inclusionsrespectively in the initial and later stages of development.The former are probably involved in the production of thesematerials. It is suggested that the proteins are directly secretedby rough ER compartments whereas smooth ER is involved in thesynthesis of lipidic materials. The carbohydrate moiety of theexudate is released by the eccrine mode (sugar mono- and dimers)with some addition of polymers by disintegration of the middlelamellae. The means by which the lipidic and osmiophilic materialis extruded remains unclear. Nicotiana sylvestris, stigma receptivity, organization, stigmatic secretory system, stigmatic exudate     

Some observations on coleoptile cell ultrastructure in ungerminated grains of rice (Oryza sativa L)

Summary The ultrastructure of coleoptile cells of ungerminated rice grains has been examined following fixation in glutaraldehyde and osmium tetroxide. In many respects the cell structure resembles that reported for other dormant seed tissues: the cells contain protein bodies and lipid droplets, mitochondria and plastids show little internal structure but cytoplasm invaginates into many plastids; golgi cisternae cannot be discerned. Rough ER is present as cisternae surrounding protein bodies, as occasional regions of parallel layers, and in concentric whorls where it alternates with smooth paired membranes of an unknown nature. The ribosomes on the ER are at least partly arranged into regular rows. Various crystalline, presumably proteinaceous, inclusions lie in the groundplasm, plastids and nuclei.     

Structure and ultrastructure of leaf and calyx glands in Galphimia brasiliensis (Malpighiaceae)

The present study describes the anatomical structure of calyx and leaf glands in Galphimia brasiliensis and analyzes the mechanism of secretion. The glands are marginal and suprabasal, cup-shaped, sessile, and scarcely visible with the naked eye. Light microscopy reveals the following features: a thin, smooth cuticle; unistratified secretory cells; subglandular parenchyma; and vascular bundle supply composed of phloem and xylem with abundant druses of calcium oxalate. Transmission electron microscopy reveals the presence of secretory cells with conspicuous nuclei, dense cytoplasm, lipid droplets, numerous vesicles, mitochondria, Golgi, rough endoplasmic reticulum (RER), and elongated plastids with osmiophilic contents. The secretion reaches the apoplastic space and accumulates beneath the cuticle. Finally, the viscous, translucent exudate is eliminated by mechanical rupture of the cuticle. Histochemical analysis confirms that lipids are the main constituent. Small amounts of polysaccharides were also identified.     

The ependymal secretion of the fetal and adult rat subcommissural organ. morphological aspects linked to the synthesis,storage and release of the secretory products

Different localizations of secretory material are noted in adult and fetal subcommissural organ (SCO) in light microscopy. At the electron microscope level, the secretory ependymocytes reveal frequent associations among mitochondria and ribosomes of the endoplasmic reticulum (ER). In the SCO ependymocytes of the adult rat, the relationship between mitochondria and ribosomes of the ER is observed in the subgolgian zone, the ER cisternal profiles are smooth except where they face the mitochondria. Here, a constant interval of 40-45 nm separates the ribosome-coated ER membrane from the external membrane of the mitochondria. This association evidences a functional cooperation between mitochondria and ER, at least in some phases of the synthesis of the organ's gliosecretory material. By contrast, in the fetus (17-21 fetal day), the synthetic apparatus displays an entirely granular ER. The secretory products are stored as flocculent material which fills the ER cisternae. In the apical zone of the ependymocytes, as the membrane of the dense secretory granules fuses with the apical plasmalemma, the granules release their contents into the ventricular cavity. A possible link between the releasing process and the coated vesicles is discussed.     

ULTRASTRUCTURAL DEVELOPMENT OF CAPITATE GLANDULAR HAIRS OF CANNABIS SATIVA L. (CANNABACEAE)

The capitate-sessile and capitate-stalked glands of the glandular secretory system in Cannabis, which are interpreted as lipophilic type glandular hairs, were studied from floral bracts of pistillate plants. These glands develop a flattened multicellular disc of secretory cells, which with the extruded secretory product forms the gland head and the auxiliary cells which support the gland head. The secretory product accumulates beneath a sheath derived from separation of the outer wall surface of the cellular disc. The ultrastructure of secretory cells in pre-secretory stages is characterized by a dense ground plasm, transitory lipid bodies and fibrillar material, and well developed endoplasmic reticulum. Dictyosomes and dictyosome-derived secretory vesicles are present, but never abundant. Secretory stages of gland development are characterized by abundant mitochondria and leucoplasts and by a large vacuolar system. Production of the secretory product is associated with plastids which increase in number and structural complexity. The plastids develop a paracrystalline body which nearly fills the mature plastid. Material interpreted as a secretion appears at the surface of plastids, migrates, and accumulates along the cell surface adjoining the secretory cavity. Extrusion of the material into the secretory cavity occurs directly through the plasma membrane-cell wall barrier.     

Rapid separation of the plastid,mitochondrial, and cytoplasmic fractions from intact leaf protoplasts of Avena

Purified intact protoplasts were isolated from etiolated and greening leaves of Avena sativa. They were ruptured by forcing them through a 20-m aperture nylon net and immediately thereafter fractionated into a pure pellet of plastids (well above 70% of total plastids), a layer of mitochondria only slightly contaminated by other cellular constituents (about 50% of total mitochondria), and a cytoplasmic supernatant. This was achieved within 60 s by an integrated method of homogenation of protoplasts and centrifugal filtration of the homogenate on a gradient of silicone oils, contained together with the nylon net in 450 l microtubes, and verified by comparing the levels of activity of specific markers within the three fractions obtained. With appropriate modifications to immediately quench metabolic reactions within the fractions, this method allows the determination of metabolite levels within plastids, mitochondria, and the cytoplasmic compartment of intact protoplasts. The applicability of this technique is demonstrated by the determination of ATP in the plastids, mitochondria, and the cytoplasm of protoplasts obtained from etiolated and greening primary leaves of Avena. The levels of ATP, corrected for contamination of the fractions by each other, exhibit a pronounced transient increase during greening, especially within the cytoplasm.Abbreviations BSA bovine serum albumin - Cyt c cytochrome c - EDTA ethylenediamine tetraacetic acid - HEPES N-2-hydroxyethyl-piperazine-N-2-ethane sulphonic acid - MES 2(N-morpholino) ethane sulphonic acid - PGA 3-phosphoglyceric acid - PEP phosphoenol pyruvic acid - RuBP ribulose-1.5-bis-phosphate     

扁豆成熟胚囊的超微结构

本文对扁豆（Dolichos lablab)成熟胚囊的超微结构进行了研究,在成熟胚囊中,卵细胞和助细胞仅在珠孔端1／3有细胞壁,靠近合点端,卵细胞一助细胞,卵细胞－中央细胞,助细胞－中央细胞之间没有细胞壁存在,相邻细胞的质膜靠在一起,在卵细胞和中央细胞的质膜间,有些地方存在中等电子密度的物质,卵细胞的细胞质中含有很多的线粒体和质体,内质网和高尔基体较少,助细胞的珠孔端有一复杂的丝状器,靠近珠孔端的细胞质中有很多管状的内质网,表明助细胞可能具有分泌功能,在助细胞的合点端,含有丰富的粗糙内质网,助细胞和卵细胞的质膜之间有很多囊泡状的结构,中央细胞内含有丰富的线粒体,高尔基体和内质网,中央细胞的壁向内形成突起,在周缘细胞质中含有丰富的脂滴。     

Mitochondrial and secretory human cytomegalovirus UL37 proteins traffic into mitochondrion-associated membranes of human cells

The human cytomegalovirus (HCMV) UL37 exon 1 protein (pUL37x1), also known as vMIA, is the predominant UL37 isoform during permissive infection. pUL37x1 is a potent antiapoptotic protein, which prevents cytochrome c release from mitochondria. The UL37x1 NH₂-terminal bipartite localization signal, which remains uncleaved, targets UL37 proteins to the endoplasmic reticulum (ER) and then to mitochondria. Based upon our findings, we hypothesized that pUL37x1 traffics from the ER to mitochondria through direct contacts between the two organelles, provided by mitochondrion-associated membranes (MAMs). To facilitate its identification, we cloned and tagged the human phosphatidylserine synthase 1 (huPSS-1) cDNA, whose mouse homologue localizes almost exclusively in the MAM. Using subcellular fractionation of stable HeLa cell transfectants expressing mEGFP-huPSS-1, we found that HCMV pUL37x1 is present in purified microsomes, mitochondria, and MAM fractions. We further examined the trafficking of the full-length UL37 glycoprotein cleavage products, which divergently traffic either through the secretory apparatus or into mitochondria. Surprisingly, pUL37_NH2 and gpUL37_COOH were both detected in the ER and MAM fraction, even though only pUL37_NH2 is preferentially imported into mitochondria but gpUL37_COOH is not. To determine the sequences required for MAM importation, we examined pUL37x1 mutants that were partially defective for mitochondrial importation. Deletion mutants of the NH₂-terminal UL37x1 mitochondrial localization signal were reduced in trafficking into the MAM, indicating partial overlap of MAM and mitochondrial targeting signals. Taken together, these results suggest that HCMV UL37 proteins traffic from the ER into the MAM, where they are sorted into either the secretory pathway or to mitochondrial importation.