Biochemical and Structural Analyses of Microtubules in the Pellicular Membrane of Leishmania tropica1

The structure of the major protein of the pellicular membrane of Leishmania tropica was investigated. This protein is composed of two polypeptides, of ca. 50,000 d molecular weight, that were found to cross-react immunologically with the α and β subunits of pig brain tubulin. The polypeptides and pig brain tubulin subunits were partially digested with S. aureus V8 protease, and the peptides obtained analysed by SDS-polyacrylamide gel electrophoresis. A comparison of the patterns showed that the β subunits of Leishmania and pig tubulin have very similar primary structures, while the α subunits have evolved divergently. These experiments demonstrate that the major polypeptides found in the pellicular membrane of L. tropica are α and β subunits of tubulin. Immuno-electron microscopy indicates that the tubulin is located in the microtubules associated with the pellicular membrane of Leishmania. Arrays of microtubules were prepared by nonionic detergent treatment of the cells and observed by electron microscopy after negative staining. Optical diffraction reveals a 5 nm spacing between protofilaments in the microtubule and a 4 nm axial periodicity corresponding to the tubulin subunits. The pitch of the shallow left-hand three-start helix is 12°. A distance of 47 nm separates each microtubule from the next. These data show that the dimensions and supramolecular organization of the tubulin subunits in the microtubules are identical in the pellicular membrane of L. tropica and in mammalian brain.     

Control of the Corpora Allata During a Reproductive Cycle in a Viviparous Cockroach

SYNOPSIS. This paper describes factors which regulate the corporaallata (CA) during the reproductive cycle in the viviparouscockroach Diploptera punctata. Experiments, designed to alterthe rate of juvenile hormone (JH) synthesis by the CA, are performedon whole animals and their effects are demonstrated by an invitro radiochemical assay for JH synthesis by the CA. The CAis both inhibited and stimulated. Axonal pathways from the brainto the CA are required for inhibition of the CA in virgin femalesbut not in young pregnant females. Humorally transmitted inhibitionof the CA is caused in vivo by JH (in high titers) and ecdysteroidhormone. JH in low titers also stimulates the CA. Since thesehormones do not affect the CA in vitro we suggest that theyexert their effect via the central nervous system. The ovary,a possible source of ecdysteroids in the hemolymph, is necessaryboth for maintenance of JH synthesis and for inhibition in therate of JH synthesis at the end of egg growth.     

Host range, purification and some properties of two carlaviruses from hop (Humulus lupulus): hop latent and American hop latent

Hop latent virus (HLV) occurs in virtually all commercial hop plants in England, without causing apparent symptoms. It was transmitted between hop plants in a non-persistent manner by the aphid Phorodon humuli, but was not seed-borne in hop. The virus infected six species in four families out of 40 in 13 families which were inoculated, but infection was systemic only in Dianthus deltoides and hop. Only Phaseolus vulgaris and Chenopodium murale developed symptoms. Purification of HLV from hop extracts was hampered by aggregation of virus particles but this was minimised either by resuspending pellets in phosphate-buffered saline containing Tween 20 or by avoiding ultra-centrifugation. Virus was purified from extracts treated with Triton X-100 by precipitation with polyethylene glycol (PEG) followed either by centrifugation through sucrose density gradients or by exclusion chromatography through columns of Sephadex G-25 and Sepharose 4B. Purified preparations contained filamentous particles c. 675 × 14 nm composed of c. 6% single stranded RNA of mol. wt c. 2.9 × 10⁶ and a single protein species of mol. wt c 33 000. Immunosorbent electron microscopy (IEM) decoration tests suggested that HLV was serologically related to carnation latent, Helenium virus S, lily symptomless and Nerine latent viruses. American hop latent virus (AHLV) was found in two introductions to England from Corvallis, USA in 1975 and 1976. It was transmitted between hop plants in the non-persistent manner by P. humuli. The virus infected 17 species in seven families out of 41 species in 13 families which were mechanically inoculated and was systemic in nine species. It did not cause symptoms in any of five English hop cultivars. C. quinoa was a convenient propagation host and countable local necrotic lesions and ringspots occurred in leaves of Datura stramonium. AHLV was purified by PEG precipitation and centrifugation in sucrose density gradients. Preparations contained filamentous particles c. 680 × 15 nm composed of c. 6% single-stranded RNA of mol. wt c. 3.0 × 10⁶ and a single protein species of mol. wt c. 33 000. In IEM decoration tests AHLV was serologically related to Nerine latent virus but did not react with antisera to 14 other carlaviruses.     

Differential behavioural responses of mayflies from streams with and without fish to trout odour

1. In streams, mayflies (Order Ephemeroptera) are at risk from fish feeding visually in the water column. The effect of fish odour on the behaviour of Baetis bicaudatus from a fishless stream and a trout stream was investigated in four large oval tanks supplied with water from the fishless stream.
2. For each mayfly population, mayfly positioning on the substratum and movement in the water column (drift) were measured during the day and night, over 3 days. Brook trout ( Salvelinus fontinalis ) odour was added to two tanks to test the effect of a threat from fish.
3. Throughout the experiment more mayflies from the trout stream were observed on the substratum surface and in the water column during the night than the day, but the magnitude of night drift was less in tanks with fish odour.
4. Baetis from the fishless stream also displayed a nocturnal periodicity in drift and positioning, but their night-time drift was not affected by the presence of fish odour. On the first day of the experiment, however, more mayflies were observed on the substratum surface and drifting in tanks without fish odour during the day.
5. Sensitivity to fish odour may enable mayflies to alter their behaviour according to the risk of predation from fish.     

Some effects of hop latent viroid on two cultivars of hop (Humulus lupulus) in the UK

Some effects of infection by hop latent viroid (HLVd) on two commercial plantings of hop, one each of two high alpha-acid cultivars, are described. The cultivar Omega was severely affected: yield of cones and individual cone weights from infected plants were both lower than from uninfected plants by c. 35% and the alpha-acids content (as assessed by HPLC) of the cones c. 30% lower. Wye Northdown was less severely affected: cone weight was 8% less (though this was not statistically significant) and alpha-acids content lower by c. 15%. In both cultivars beta-acids were higher in infected plants which, together with differences in other chemical components, suggested that cones on infected plants had matured, or were maturing, earlier than those on uninfected plants. These effects, together with the previous finding that HLVd occurs frequently in some cultivars (Barbara, Morton & Adams, 1990), suggest that HLVd is a potentially important constraint on hop production in the UK and should be eliminated if possible.     

Crystal Structure of the C-Terminal Tetrapeptide of Oxytocin

WE have determined the crystal structure of the protected, C-terminal tetrapeptide of oxytocin S-benzyl-L-cysteinyl-L-prolyl-L-leucyl-glycine amide as well as of its virtually isomorphous seleno-analogue. The crystal structure analyses of these two peptides were undertaken because of our interest in the conformation of the tetrapeptide in isolation as well as when attached to the ring in the complete oxytocin molecule. The seleno-analogue provided an opportunity to compare sulphur and selenium stereochemistry.     

The Ultrastructure of Vampyrellidium perforans Surek & Melkonian and Its Taxonomic Position Among the Naked Filose Amoebae1

An account of the fine structure of Vampyrellidium perforans is given. The organism has filose pseudopodia, mitochondria with flattened cristae, and cytoplasmic microtubules, some of which arise from a perinuclear cytoplasmic sheath. Microtubules were observed within nuclei presumed to be at an early stage of division. Relatively massive (non-filose) pseudopodia are formed by cells feeding by engulfment. The cytoplasm of these pseudopodia has a fibrillar consistency with local aggregations of material. Despite sharing aspects of feeding behavior with vampyrellid filose amoebae, Vampyrellidium perforans is ultrastructurally more similar to Nuclearia , and it is here assigned to nucleariid filose amoebae.     

Rapid Growth of Acanthamoeba In Defined Media; Induction of Encystment By Glucose-Acetate Starvation

Defined media are described that support 14-20 h generation times for Acanthamoeba castellanii and A. rhysodes in monolayer cultures. the media differ in minor ways from previously described media, but the growth rates are greatly improved over previously reported values. Maximum growth rates were observed for A, castellanii in a complex medium containing 21 amino acids, but near-maximum rates could be achieved in relatively simple media containing 9 amino acids. Growth occurred with 6 amino acids, as reported by others, but generation times exceeded 30 h. Amitosis was a common problem during early subcultures in defined media, but became infrequent after repeated transfers. Synchronous encystment resulting in 70-80% cyst formation could be induced in the defined media by glucose and acetate starvation. the rate of encystment varied with cell density at the time of starvation and was optimal at initial densities of 400-800 amebae/mm2.     

TEWA KINSHIP TERMS FROM THE PUEBLO OF HANO, ARIZONA

Late Research Fellow and Mary-Ewart Scholar of Somerville College, Oxford, England; student attached to the School of American Archaeology, Santa Fe, New Mexico.