A novel milky disease organism from Australian scarabaeids: Ultrastructure

The unusual ultrastructure of a milky disease bacterium isolated from Aphodius tasmaniae is described and compared with a similar bacterium from Tipula paludosa. Both organisms possess an elongate sporangium with a small central spore, a multilayered exosporium, and longitudinally arranged extrasporal fibrils which arise from plates attached to the ends of the spore. The morphogenesis of the sporangium is described and illustrated for the organism from A. tasmaniae. It is suggested this organism and that from T. paludosa are closely related. Their taxonomic position remains obscure.     

Characterization of a low density cytoplasmic membrane subfraction isolated from Escherichia coli

We have used freeze fracture electron microscopy to study the distribution of membrane proteins in the cytoplasmic membrane of Escherichia coli W 3110. While these proteins were distributed randomly at the growth temperature (37 °C), there was extensive protein lipid segregation when the temperature was lowered, resulting in bare patches containing no visible particles (protein), and areas of tightly packed or aggregated particles. To understand the segregation process, we have separated the bare patches from the particle rich membrane areas. Lysis of spheroplasts at 0 °C leads to cytoplasmic membrane fragments with different amounts of membrane particles per unit area; such fragments have been separated on isopycnic sucrose gradients. The bare patches occurred as low density membranes which were completely devoid of particles. They were compared to normal density cytoplasmic membranes with respect to fatty acid composition, protein distribution as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and their content of several cytoplasmic membrane marker enzymes.The phospholipid to protein ratio of low density membranes was five times greater than that of normal membranes; unsaturated fatty acids were more abundant in the low density membranes. Most proteins had disappeared from the low density membranes. One protein, which had an apparent molecular weight of 26000 on sodium dodecyl sulfate gels appeared to be concentrated in the low density membranes; it accounted for about 50% of the total protein found in this membrane fraction.Of the cytoplasmic membrane markers tested, NADH oxidase and succinate dehydrogenase were excluded, while d-lactate dehydrogenase remained, and even appeared to be concentrated in the low density membranes.These results indicate that while most membrane proteins are associated with the fluid portion of the bilayer, some proteins evidently associate preferentially with phospholipids in the gel or frozen state.     

Binding of Cyt1Aa and Cry11Aa Toxins of Bacillus thuringiensis Serovar israelensis to Brush Border Membrane Vesicles of Tipula paludosa (Diptera: Nematocera) and Subsequent Pore Formation

Bacillus thuringiensis serovar israelensis (B. thuringiensis subsp. israelensis) produces four insecticidal crystal proteins (ICPs) (Cry4A, Cry4B, Cry11A, and Cyt1A). Toxicity of recombinant B. thuringiensis subsp. israelensis strains expressing only one of the toxins was determined with first instars of Tipula paludosa (Diptera: Nematocera). Cyt1A was the most toxic protein, whereas Cry4A, Cry4B, and Cry11A were virtually nontoxic. Synergistic effects were recorded when Cry4A and/or Cry4B was combined with Cyt1A but not with Cry11A. The binding and pore formation are key steps in the mode of action of B. thuringiensis subsp. israelensis ICPs. Binding and pore-forming activity of Cry11Aa, which is the most toxic protein against mosquitoes, and Cyt1Aa to brush border membrane vesicles (BBMVs) of T. paludosa were analyzed. Solubilization of Cry11Aa resulted in two fragments, with apparent molecular masses of 32 and 36 kDa. No binding of the 36-kDa fragment to T. paludosa BBMVs was detected, whereas the 32-kDa fragment bound to T. paludosa BBMVs. Only a partial reduction of binding of this fragment was observed in competition experiments, indicating a low specificity of the binding. In contrast to results for mosquitoes, the Cyt1Aa protein bound specifically to the BBMVs of T. paludosa, suggesting an insecticidal mechanism based on a receptor-mediated action, as described for Cry proteins. Cry11Aa and Cyt1Aa toxins were both able to produce pores in T. paludosa BBMVs. Protease treatment with trypsin and proteinase K, previously reported to activate Cry11Aa and Cyt1Aa toxins, respectively, had the opposite effect. A higher efficiency in pore formation was observed when Cyt1A was proteinase K treated, while the activity of trypsin-treated Cry11Aa was reduced. Results on binding and pore formation are consistent with results on ICP toxicity and synergistic effect with Cyt1Aa in T. paludosa.     

Factors Controlling the Production of Lysogenic Cultures of B. megatherium

(1) The proportion of infected B. megatherium cells which develop lysogenic colonies depends on the number and kind of infecting virus particles and on the culture medium in which the cells are growing. (2) Cells infected with 100 or more T virus particles (from megatherium 899) in yeast extract peptone disintegrate, produce very few virus particles, and less than one lysogenic colony per 10⁷ infected cells. Cells infected with one or a few particles produce 500 to 1000 virus particles each and about 30 lysogenic colonies per 10⁷ infected colonies. (3) T phage obtained from lysogenic magatherium KM cultures produces many more lysogenic cells than does the original megatherium 899 virus. (4) Cells infected with megatherium 899 T virus in peptone medium and then transferred to asparagine medium give rise to 10⁶ lysogenic colonies per 10⁷ infected cells and this transformation will occur even after the infected cells have been in peptone for 60 to 90 minutes and are beginning to produce virus particles. (5) Continued growth of KM strain with either C or T virus from megatherium 899 for several hundred generations in the steady state apparatus results in a lysogenic strain which produces several different types of virus.     

Membranous cytochrome c oxidase. A freeze-fracture electron microscopic analysis

Suspensions of membranous cytochrome c oxidase prepared from beef heart mitochondria by Triton extraction were ultra-rapidly cooled (in excess of 10,000 deg.C/s) and analyzed using freeze-fracture and freeze-fracture-etch techniques. The preparations contained non-crystalline and crystalline vesicles as isolated vesicles, vesicles inside other vesicles and stacks of vesicles. In non-crystalline vesicles the particles (about 100 Å diameter) are probably formed by the deviation of hydrophobic fracture planes of the membranes around the large transmembrane enzymes. The intramembrane particles thus formed are compared to particles (about 80 Å diameter) in a vesicle reconstituted from purified enzyme and lipid. Crystalline membranous cytochrome c oxidase vesicles display an unusual fracture pattern in which adjacent crystalline surfaces are separated from each other and from the surrounding ice by fracture steps that are approximately the thickness of a single membrane (100 to 120 Å). In addition adjacent crystalline fracture surfaces have similar low-relief textures, both of which differ significantly from the hydrophobic surfaces normally exposed in membrane fractures. This fracture morphology is interpreted in terms of fractures along hydrophilic surfaces of the membranes. Images of etched crystalline vesicles provide support for this interpretation because etching exposes no new surfaces. It is concluded that the crystalline lattices are derived from the portions of enzymes that protrude from the membrane bilayers and that the interdigitation of the enzymes on the inside surfaces of the vesicles or between vesicles determines the appearance of the crystalline surfaces. The arrangement of the tails of the y-shaped molecules on the cytoplasmic sides of the crystalline membranes can be visualized in micrographs directly and in reconstructions of filtered images. The more complex pattern of arms protruding on the matrix side is obscured by the unidirectional shadowing. Fragmentation of the crystalline membranes during fracturing is indicated by particles sometimes present at the edges of fractured membranes and by deep, irregular pits observed in crystalline surfaces. Particles resting on some crystalline surfaces may be fragments of crystalline membranes removed during fracturing. In other crystalline membranes non-protein is removed during fracturing, leaving globular particles embedded in the lattice, which measure about 118 Å diameter. Comparing these particles to the 3-dimensional arrangement of protein described in the accompanying paper (Frey et al., 1982) suggests that such particles are composed of 2 dimers paired along the a-axis. Intramembrane and fragmentation particles of similar size may also have this protein composition.     

THE STRUCTURE OF SOME CYTOPLASMIC COMPONENTS OF PLANT CELLS IN RELATION TO THE BIOCHEMICAL PROPERTIES OF ISOLATED PARTICLES

1. Electron micrographs of thin sections of material fixed with buffered osmium tetroxide have been used for comparison of the fine structure of isolated cytoplasmic particles from silver beet petioles and roots of germinating wheat with that of the cytoplasm of the intact cells. 2. Mitochondria of wheat roots have an external double membrane and poorly oriented internal double membranes. As compared with the structures seen in situ, the isolated mitochondria showed evidence of some disorganisation of the fine internal structure, probably due to osmotic effects. The possible influence of such changes on the enzymic properties of the isolated mitochondria is discussed. 3. The isolated plant microsomes are mainly spherical vesicular structures consisting of (a) an outer membrane enclosing (b) either an homogeneous slightly dense material (wheat root microsomes) or some granular dense material (silver beet microsomes) and (c) small dense particles, mostly associated with the vesicle membranes. 4. The cytoplasm of the wheat root cells does not contain any structures similar to the isolated microsomes but has a very dense reticular network, consisting of membranes with associated small dense particles, here called the endoplasmic reticulum. The observations indicate that the isolated microsomes arise mainly by rupture and transformation of the membranes of this structure. The effects of such extensive changes in the lipoprotein membranes on the enzymic activities of the endoplasmic reticulum, as studied in isolated microsomes, is discussed. 5. Meristematic wheat root cells contain structures which consist of smooth membranes with associated vacuoles and are similar to the Golgi zones of animal cells. The membranes of these zones probably contribute to the microsomal fraction under the conditions of preparation used for the enzymic and chemical studies previously reported.     

Mitrula aurea sp. nov., A New Aero-Aquatic Species from the Republic of Korea

The genus Mitrula (Mitrulaceae, Helotiales), as also known as swamp beacons, inhabits submerged, decaying vegetation in standing or decaying needles, twigs, leaves, and shallow water. They play an important role in carbon cycling in some freshwater ecosystems. In the herbarium of the Korea National Arboretum (KH), seven Mitrula specimens were collected during mushroom forays in the period from 2019 to 2021. The Korean collections were found to be macromorphologically closely related to M. paludosa and M. elegans, but micromorphologically they could be distinguished by characteristics of slightly narrower asci and aseptate ascospores. Our molecular phylogenetic analyses of the internal transcribed spacer (ITS) and 28S rDNA regions also revealed that our specimens were related to M. paludosa and M. elegans, but formed a distinct clade. Based on these results, we reported our specimens as new to science and discussed the phylogeny and diversity of Mitrula species.     

A freeze fracture and thin section study of intestinal cell membranes and intercellular junctions of a nematode, Ascaris

The microvillar and lumenal plasma membrane P-face of Ascaris intestinal cells is shown to be covered by relatively large (13 nm) particles at a fairly high density (1000/μm²), while the E-face has virtually none. The P-face of the lateral cell membranes, those separating the cells, have fewer and smaller (8 nm) particles. The intestinal cells are also shown to be connected by an apical complex of smooth septate and tricellular junctions similar to those found between some insect midgut cells. A periodic layer of tannic acid staining material is found on the cytoplasmic sides of the smooth septate junction, and when the intercellular space is filled with lanthanum, smoothly curved, 10 nm wide septal walls can be seen. Below the belt of septate junctions are a large number of gap junctions. These have closely packed arrays of particles on the P-face with some particle aggregates adhering to the closely packed pit arrays on the E-face.     

Virus particle packaging in baculovirus and cytoplasmic polyhedrosis virus inclusion bodies

The structure of the inclusion bodies (IBs) of three multiply enveloped nuclear polyhedrosis viruses (MNPVs), one singly enveloped NPV (SNPV), two granulosis viruses (GVs) and one cytoplasmic polyhedrosis virus (CPV) were compared. A method was devised to calculate the numbers of virus particles and nucleocapsids in IBs using data from light microscopy and thin sections. The three MNPVs, from Agrotis segetum (English and Polish virus isolates) and Mamestra brassicae had similar concentrations of virus particles ranging from 17.3 to 19.6 per μm³ of IB. Plusia gamma SNPV had a higher density of 59.6 virus particles per μm³ of IB, which partly compensated for its having smaller IBs (mean volume 0.65 μm³) than the MNPVs (2.60–9.71 μm³). The English A. segetum MNPV isolate had the most nucleocapsids in each virus particle (mean, 4.04) and the largest IBs (mean volume, 9.71 μm³), giving 674 nucleocapsids per IB on average. The GVs, from A. segetum and Pieris brassicae, mainly contained one nucleocapsid per IB. P. gamma CPV IBs had a much higher density of virus particles than the baculoviruses (260 per μm³ compared with 17–60 per μm³). These data are discussed in relation to the biological properties of these viruses, and possible adaptational advantages of alternative IB designs are considered.     

Evidence of a climatic niche shift following North American introductions of two crane flies (Diptera; genus Tipula)

Ecological niche models assume a species niche should be conserved over space and time. Increasingly, studies have determined that niche shifts may occur during biological invasion events. The aim of this study is to examine niche conservation for two invasive crane flies, Tipula oleracea Linnaeus and Tipula paludosa Meigen, after introductions into North America. These species have broadly sympatric invasive distributions but differ in time since introduction and dispersal abilities. As these factors may impact the area accessible to dispersal, I examined the impact of background area delineation on conclusions of niche conservation. Results indicated that alternative delineations of accessible area (i.e., background area) had no affect on measures of niche equivalence. Neither Tipula species was found to be occupying invasive niche space equivalent to that of their native ranges. Niche dissimilarity was found for both species, with results strongly impacted by the choice of background area. T. paludosa introductions displayed a niche shift across both invasive introductions when the model area drew climatic information from an area that buffered occurrences by 40 km. The eastern T. oleracea introduction displayed a niche shift when background information was drawn from within a 400 km buffered area. This study suggests that invasive populations may be displaying a niche shift when evaluated against one scale of background but conserved when evaluated against another scale. Dispersal limitations for T. oleracea in its eastern introduction and anthropogenic habitat associations for T. paludosa across both invasive introductions are indicated as causes for the observed niche shifts. The results of this study highlight the importance of carefully delineating the area accessible to invasive species in studies of niche conservation. Furthermore, it indicates that examining several spatial extents of background areas can be beneficial when examining niche conservation for species in non-equilibrium states.     

Changes in amino-terminal sequences of pp60src lead to decreased membrane association and decreased in vivo tumorigenicity

We have suggested previously that the amino-terminal 8 kilodaltons of pp60^src may serve as a structural hydrophobic domain through which pp60^src attaches to plasma membranes. Two isolates of recovered avian sarcoma viruses (rASVs), 1702 and 157, encode pp60^src proteins that have alterations in this amino-terminal region. The rASV 1702 src protein (56 kilodaltons) and the 157 src protein (62.5 kilodaltons) show altered membrane association, and fractionate largely as soluble, cytoplasmic proteins in aqueous buffers, in contrast with the membrane association of more than 80% of the src protein of standard avian sarcoma virus under the identical fractionation procedure. Plasma membranes purified from cells transformed by these rASVs contain less than 10% of the amount of pp60^src found in membranes purified from cells transformed by Rous sarcoma virus or control rASVs. The altered membrane association of these src proteins had little or no effect on the properties of chick embryo fibroblasts transformed in monolayer culture. In contrast, rASV 1702 showed reduced in vivo tumorigenicity compared with Rous sarcoma virus or with other rASVs that encode membrane-associated src proteins. Rous sarcoma virus-induced tumors are malignant, poorly differentiated sarcomas that are lethal to their hosts. rASV 1702 induces a benign, differentiated sarcoma that regresses and is not lethal to its hosts. These data support the role of amino-terminal sequences in the membrane association of pp60^src, and suggest that the amino terminus of pp60^src may have a critical role in the promotion of in vivo tumorigenicity.     

Digestion and excretion of nitrogen and carbohydrate by the cranefly larva Tipula paludosa (Diptera: Tipulidae)

The nitrogenous and carbohydrate components of ryegrass and faeces from larvae of Tipula paludosa Meigen, fed on ryegrass (Lolium perenne L.), were compared. Proteins in ryegrass were efficiently digested and uric acid was the major nitrogenous excretory product. The alkaline midgut (pH 9.1) was considered to enhance the digestibility of hemicellulose, by removing inhibitory acetyl groups, and of cellulose by altering its crystallinity. T. paludosa larvae assimilated 50% of ryegrass cellulose, and 50% of an isolated ¹⁴C-labelled cellulose, whereas 86% of hemicellulose was digested.     

N-terminal polyhedrin sequences and occludedBaculovirus evolution

Summary A phylogenetic tree for occluded baculoviruses was constructed based on the N-terminal amino acid sequence of occlusion body proteins from six baculoviruses including three lepidopteran nuclear polyhedrosis viruses (NPVs), [two unicapsid (Bombyx mori andOrgyia pseudotsugata) and one multicapsid (Orgyia pseudotsugata)]; one granulosis virus (Pieris brassicae); and NPVs from a hymenopteran (Neodiprion sertifer) and a dipteran (Tipula paludosa). Amino acid sequence data for theB. mori NPV were from a report by Sere-bryani et al. (1977) and that for theO. pseudotsugata NPVs were reported previously by us (Rohrmann et al. 1979). The other N-terminal amino acid sequences are presented in this paper. The phylogenetic relationships determined based on the molecular evolution of polyhedrin were also investigated by antigenic comparisons of the proteins using a solid phase radioimmune assay. The results indicate that the lepidopteran NPVs are the most closely related of the above group of viruses and are related to these viruses in the following order:N. sertifer NPV,P. brassicae granulosis virus, andT. paludosa NPV. These data, in conjunction withBaculovirus distribution and evidence concerning insect phylogeny, suggest that theBaculovirus have an ancient association with insects and may have evolved along with them.     

A new natural α-helical peptide from the venom of the scorpion Heterometrus petersii kills HCV

Hepatitis C virus (HCV) is a major cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma. There is no vaccine available for HCV, and almost half of patients cannot be cured using standard combination therapy. Thus, new anti-HCV strategies and drugs are urgently needed. Here, the gene encoding a new α-helical peptide, Hp1090, was screened from the venomous gland cDNA library of the scorpion Heterometrus petersii. Structural analysis showed that Hp1090 is an amphipathic α-helical peptide. In vitro HCV RNA inhibitory assays indicated that Hp1090 peptide inhibited HCV infection with an IC₅₀ of 7.62 μg/ml (5.0 μM), whereas Hp1035 peptide, showing high homology to Hp1090, exhibited no anti-HCV activity. Hp1090 acted as a viricide against HCV particles in vitro and prevented the initiation of HCV infection. Furthermore, this peptide interacted with HCV particles directly and rapidly permeabilized phospholipid membranes. Collectively, it seems that Hp1090 is virocidal for HCV in vitro, directly interacting with the viral membrane and decreasing the virus infectivity. These results suggest that Hp1090 could be considered an anti-HCV lead compound with virocidal mechanism that offers a potential therapeutic approach to HCV infection. Our work opens a new avenue for antiviral drug discovery in natural scorpion venom.     

The incidence of Rasajeyna nannyla in Tipula paludosa and Tipula vittata at two sites in Northumberland,England

Rasajeyna nannyla was an established pathogen at the two sample sites, and under the relatively constant conditions during two seasons, there was little change in the incidence of this pathogen. The incidence of R. nannyla was higher in Tipula vittata, a leatherjacket inhabiting damp regions of the sample sites, than in T. paludosa which inhabits drier regions. Monthly fluctuations of the level of R. nannyla in leatherjackets were not related to monthly variations in temperature. The incidence of R. nannyla in T. paludosa as a function of temperature is a significant positive slope, whereas the incidence of R. nannyla in T. vittata as a function of temperature is a significant negative slope.     

Minimal Features of Efficient Incorporation of the Hemagglutinin-Neuraminidase Protein into Sendai Virus Particles

Two transmembrane glycoproteins form spikes on the surface of Sendai virus, a member of the Respirovirus genus of the Paramyxovirinae subfamily of the Paramyxoviridae family: the hemagglutinin-neuraminidase (HN) and the fusion (F) proteins. HN, in contrast to F, is dispensable for viral particle production, as normal amounts of particles can be produced with highly reduced levels of HN. This HN reduction can result from mutation of an SYWST motif in its cytoplasmic tail to AFYKD. HN_AFYKD accumulates at the infected cell surface but does not get incorporated into particles. In this work, we derived experimental tools to rescue HN_AFYKD incorporation. We found that coexpression of a truncated HN harboring the wild-type cytoplasmic tail, the transmembrane domain, and at most 80 amino acids of the ectodomain was sufficient to complement defective HN_AFYKD incorporation into particles. This relied on formation of disulfide-bound heterodimers carried out by the two cysteines present in the HN 80-amino-acid (aa) ectodomain. Finally, the replacement of the measles virus H cytoplasmic and transmembrane domains with the corresponding HN domains promoted measles virus H incorporation in Sendai virus particles.     

Role of rubella virus glycoprotein domains in assembly of virus-like particles

Rubella virus is a small enveloped positive-strand RNA virus that assembles on intracellular membranes in a variety of cell types. The virus structural proteins contain all of the information necessary to mediate the assembly of virus-like particles in the Golgi complex. We have recently identified intracellular retention signals within the two viral envelope glycoproteins. E2 contains a Golgi retention signal in its transmembrane domain, whereas a signal for retention in the endoplasmic reticulum has been localized to the transmembrane and cytoplasmic domains of E1 (T. C. Hobman, L. Woodward, and M. G. Farquhar, Mol. Biol. Cell 6:7-20, 1995; T. C. Hobman, H. F. Lemon, and K. Jewell, J. Virol. 71:7670-7680, 1997). In the present study, we have analyzed the role of these retention signals in the assembly of rubella virus-like particles. Deletion or replacement of these domains with analogous regions from other type I membrane glycoproteins resulted in failure of rubella virus-like particles to be secreted from transfected cells. The E1 transmembrane and cytoplasmic domains were not required for targeting of the structural proteins to the Golgi complex and, surprisingly, assembly and budding of virus particles into the lumen of this organelle; however, the resultant particles were not secreted. In contrast, replacement or alteration of the E2 transmembrane or cytoplasmic domain, respectively, abrogated the targeting of the structural proteins to the budding site, and consequently, no virion formation was observed. These results indicate that the transmembrane and cytoplasmic domains of E2 and E1 are required for early and late steps respectively in the viral assembly pathway and that rubella virus morphogenesis is very different from that of the structurally similar alphaviruses.     

ELECTRON MICROSCOPE OBSERVATIONS ON INTRACELLULAR VIRUS-LIKE PARTICLES ASSOCIATED WITH THE CELLS OF THE LUCKÉ RENAL ADENOCARCINOMA

The common renal adenocarcinoma of the leopard frog was studied in thin sections with the electron microscope. Approximately a third of the tumors examined were found to contain spheroidal bodies of uniform size and distinctive morphology that are believed to be virus particles. These consist of hollow spheres (90 to 100 mµ) having a thick capsule and a dense inner body (35 to 40 mµ) that is eccentrically placed within the central cavity (70 to 80 mµ). Virus particles of this kind occur principally in the cytoplasm but occasionally they are also found in the nucleus and in the extracellular spaces of the tumor. The intranuclear inclusion bodies that are visible with the light microscope are largely comprised of hollow, spherical vesicles with thin limiting membranes. These are embedded in a finely granular matrix. A few of the thin walled vesicles contain a dense inner body like that of the cytoplasmic virus particles. This suggests that they may be immature virus particles. The inclusion bodies are believed to be formed in the course of virus multiplication but they usually contain very few mature virus particles. Bundles of dense filaments and peculiar vacuolar inclusions also occur in the cytoplasm of the tumor cells. These seem to be related in some way to the presence of virus but their origin and significance remain obscure. These findings are discussed in relation to previous work suggesting that the Lucké adenocarcinoma is caused by an organ-specific filtrable agent. It is concluded that the "virus particles" found in electron micrographs of the tumor cells may be the postulated tumor agent. On the other hand, the possibility remains that the particles described here are not those that are causally related to the tumors.     

AN ELECTRON MICROSCOPE STUDY OF TOBACCO MOSAIC VIRUS LESIONS IN NICOTIANA GLUTINOSA L

Ultra-thin sections of Nicotiana glutinosa L. leaves inoculated with a concentrated solution of tobacco mosaic virus were made at short intervals from 0 to 78 hours after inoculation. Eight hours after inoculation, the size of starch grains increased. This was followed by rupture of cytoplasmic and chloroplast membranes. At about 24 hours there was a great increase in number of mitochondria, which persisted until about 60 hours, when some became electron opaque while others appeared to disintegrate. Finally, the cell contents were compressed into one area of the cell, where they became electron opaque. This was accompanied by collapse of the rest of the cell and tearing away of the cell walls from adjacent cells. The nucleus remained stable and intact for as long as observations could be made. No identifiable virus particles were seen.     

Narcissus latent, a virus with filamentous particles and a novel combination of properties

As previously reported, narcissus latent virus (NLV) has flexuous filamentous particles measuring c. 650 nm × 13 nm, is manually transmissible to Nicotiana clevelandii and Tetragonia expansa, and is transmitted by the aphid Myzus persicae following brief acquisition access periods. In contrast to previous reports the virus particle protein has an apparent mol. wt of c. 45 kD. Moreover, infected cells in N. clevelandii leaves contain cytoplasmic inclusion bodies resembling those of potyviruses. In vitro translation of NLV RNA produced only one major product (mol. wt c. 25 kD) which was not precipitated by antisera to virus particle protein or to cytoplasmic inclusion protein. Antisera to 12 potyviruses and nine carlaviruses failed to react with sap containing NLV particles. Similarly antiserum to NLV particles did not react with particles of seven potyviruses or four carlaviruses. A weak reaction was detected between NLV particles and antiserum to particles of maclura mosaic virus (MMV), a virus which resembles NLV in particle morphology and particle-protein size, and in inducing pinwheel inclusions. The cytoplasmic inclusion proteins (CIPs) of NLV, MMV and from narcissus plants with yellow stripe symptoms were serologically inter-related. These proteins were also serologically related to, and had mol. wt similar to, the CIP of members of the potyvirus group. Particles with the size and antigenic specificity of those of NLV were found consistently in narcissus plants with yellow stripe disease. Narcissus latent and narcissus yellow stripe viruses therefore seem to be synonymous and, together with MMV, have properties distinct from those of any previously described virus group.