Ant–aphid mutualism: the influence of ants on the aphid summer cycle

There are few longtime studies on the effects on aphids of being tended by ants. The aim of this study is to investigate how the presence of ants influences settling decisions by colonizing aphids and the post‐settlement growth and survival of aphid colonies. We conducted a field experiment using the facultative myrmecophile Aphis fabae and the ant Lasius niger. The experiment relied on natural aphid colonization of potted plants of scentless mayweed Tripleurospermum perforatum placed outdoors. Ants occurred naturally at the field site and had access to half of the pots and were prevented from accessing the remainder. The presence of winged, dispersing aphids, the growth and survival of establishing aphid colonies, and the presence of parasitoids were measured in relation to presence or absence of ants, over a period of five weeks. The presence of ants did not significantly influence the pattern of initial host plant colonization or the initial colony growth, but ant‐tended aphids were subject to higher parasitism by hymenopteran parasitoids. The net result over the experimental period was that the presence of ants decreased aphid colony productivity, measured as the number of winged summer migrants produced from the colonized host plants. This implies that aphids do not always benefit from the presence of ants, but under some conditions rather pay a cost in the form of reduced dispersal.     

Efficient transport of Semliki Forest virus glycoproteins through a Golgi complex morphologically altered by Uukuniemi virus glycoproteins.

In infected BHK21 cells, the glycoproteins G1 and G2 of a temperature-sensitive mutant (ts12) of Uukuniemi virus (UUK) accumulate at 39 degrees C in the Golgi complex (GC) causing an expansion and vacuolization of this organelle. We have studied whether such an altered Golgi complex can carry out the glycosylation and transport to the plasma membrane (PM) of the Semliki Forest virus (SFV) glycoproteins in double-infected cells. Double-immunofluorescence staining showed that approximately 90% of the cells became infected with both viruses. Almost the same final yield of infectious SFV was obtained from double-infected cells as from cells infected with SFV alone. The rate of transport from the endoplasmic reticulum (ER) via the GC to the plasma membrane of the SFV glycoproteins was analysed by immunofluorescence, surface radioimmunoassay and pulse-chase labeling followed by immunoprecipitation, endoglycosidase H digestion and SDS-PAGE. The results showed that: the SFV glycoproteins were readily transported to the cell surface in double-infected cells, whereas the UUK glycoproteins were retained in the GC; the transport to the PM was retarded by approximately 20 min, due to a delay between the ER and the central Golgi; E1 of SFV appeared at the PM in a sialylated form. These results indicate that the morphologically altered GC had retained its functional integrity to glycosylate and transport plasma membrane glycoproteins.     

Mechanism of interaction of citrate synthase with citryl-CoA

Arguments are presented which indicate that the low steady-state rates of citrate production governing the catalytic interaction of citrate synthase from pig heart with citryl-CoA reflect the formation of a non-productive enzyme.citryl-CoA complex. The kinetic predictions of such an extended reaction mechanism are examined and are shown to account in satisfactory detail for the complex multiphasic rate behaviour exhibited by the enzyme under a variety of conditions in reactions involving citryl-CoA as a substrate.     

Sequence organization of a viral DNA insertion present in the adenovirus-type-5-transfonned hamster line BHK268-C31

The hamster cell line BHK268-C31 contains two large viral inserts which both include sequences from the left-hand end of adenovirus type 5 (Ad5) DNA. One of these viral inserts has been cloned in the λ vector Charon 4A. Electron microscopic analysis and restriction enzyme mapping shows that the recombinant carries a 4.4-kb-long colinear segment of viral DNA, which is located between map positions 1.5 and 14.2 in the Ad5 genome. The junctions between viral DNA and flanking sequences have been sequenced and found not to show any specific features. One of the junctions is located in the E1 a coding region, 573 bp from the left-hand end of the Ad5 genome, whereas the other junction is situated in the coding region for polypeptide IVa2. The promoter region as well as the cap site for the mRNAs from region E la are thus missing from this insert and its role in viral transformation is unclear.     

Identification and characterization of a mammalian 14-kDa phosphohistidine phosphatase.

Protein histidine phosphorylation in eukaryotes has been sparsely studied compared to protein serine/threonine and tyrosine phosphorylation. In an attempt to rectify this by probing porcine liver cytosol with the phosphohistidine-containing peptide succinyl-Ala-His(P)-Pro-Phe-p-nitroanilide (phosphopeptide I), we observed a phosphatase activity that was insensitive towards okadaic acid and EDTA. This suggested the existence of a phosphohistidine phosphatase different from protein phosphatase 1, 2A and 2C. A 1000-fold purification to apparent homogeneity gave a 14-kDa phosphatase with a specific activity of 3 micro mol.min-1.mg-1 at pH 7.5 with 7 micro m phosphopeptide I as substrate. Partial amino-acid sequence determination of the purified porcine enzyme by MS revealed similarity with a human sequence representing a human chromosome 9 gene of hitherto unknown function. Molecular cloning from a human embryonic kidney cell cDNA-library followed by expression and purification, yielded a protein with a molecular mass of 13 700 Da, and an EDTA-insensitive phosphohistidine phosphatase activity of 9 micro mol.min-1.mg-1 towards phosphopeptide I. No detectable activity was obtained towards a set of phosphoserine-, phosphothreonine-, and phosphotyrosine peptides. Northern blot analysis indicated that the human phosphohistidine phosphatase mRNA was present preferentially in heart and skeletal muscle. These results provide a new tool for studying eukaryotic histidine phosphorylation/dephosphorylation.     

Determination and analysis of antigenic epitopes of prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2) using synthetic peptides and computer modeling.

Prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2), produced essentially by the prostate gland, are 237-amino acid monomeric proteins, with 79% identity in primary structure. Twenty-five anti-PSA monoclonal antibodies (Mabs) were studied for binding to a large array of synthetic linear peptides selected from computer models of PSA and hK2, as well as to biotinylated peptides covering the entire PSA sequence. Sixteen of the Mabs were bound to linear peptides forming four independent binding regions (I-IV). Binding region I was localized to amino acid residues 1-13 (identical sequence for PSA and hK2), II (a and b) was localized to residues 53-64, III (a and b) was localized to residues 80-91 (= kallikrein loop), and IV was localized to residues 151-164. Mabs binding to regions I and IIa were reactive with free PSA, PSA-ACT complex, and with hK2; Mabs binding to regions IIb, IIIa, and IV were reactive with free PSA and PSA-ACT complex, but unreactive with hK2; Mabs binding to region IIIb detected free PSA only. All Mabs tested (n = 7) specific for free PSA reacted with kallikrein loop (binding region IIIb). The presence of Mabs interacting with binding region I did not inhibit the catalytic activity of PSA, whereas Mabs interacting with other binding regions inhibited the catalysis. Theoretical model structures of PSA, hK2, and the PSA-ACT complex were combined with the presented data to suggest an overall orientation of PSA with regard to ACT.     

Genes for cysteine proteinases from Trypanosoma rangeli

Abstract PCR amplification of genomic DNA from the American trypanosome, Trypanosoma rangeli , using as primers oligonucleotides derived from the gene of cruzipain, the major cysteine proteinase (CP) from Trypanosoma cruzi , allowed the production of a probe which was used to obtain three clones encoding a CP with 70% overall identity with cruzipain. The genes are organized in tandem, with a monomere size of approximately 2 kbp, located on two chromosomes which, in some parasite isolates, have a high molecular mass (higher than 5.7 Mbp), and in others are much smaller (about 500 kbp). The low expression of this CP at the protein level correlates well with the low level of specific mRNA found in Northern blots.