Translation in a reticulocyte cell-free system of RNA isolated from blood and culture forms of Trypanosoma brucei

Immunoprecipitation of in vitro translation products of Fasciola hepatica RNA

Incubation of in vitro translation products of RNA isolated from Fasciola hepatica with immune rat serum and sera from infected sheep resulted in the immunoprecipitation of a number of polypeptides, most of which had similar electrophoretic mobilities. Although only one of these (a 30 kDa species) correlated precisely in mobility with that of biosynthetically labelled excretory-secretory (ES) antigens, this polypeptide (along with several others) was also immunoprecipitated by sheep sera raised against authentic ES antigens. This verified that the isolated RNA contained mRNA species encoding ES antigens of the parasite. In addition, immune rat serum immunoprecipitated a 64 kDa polypeptide which was not immunoprecipitated by infected sheep serum or anti-ES antigen sheep serum. The possible significance of this finding in terms of the ability of rats to develop resistance to fascioliasis in contrast to sheep which apparently cannot is discussed.

Characterization of the DNA duplication-transposition that controls the expression of two genes for variant surface glycoproteins in Trypanosoma brucei

The genome of Trypanosoma brucei carries over a hundred genes coding for different variants of the major surface glycoprotein. Activation of some of these genes is accompanied by a duplication and transposition of the gene (the basic copy) to another region in the genome where it is transcribed. We present here physical maps of the basic and transposition-activated genes for two surface glycoproteins of Trypanosoma brucei, stock 427. In both cases the transposed segment starts 1-2 kb in front of the coding region and ends within the 3'-terminal region of the gene. The DNA segments flanking both transposed genes are indistinguishable and share a 6-kb stretch upstream and a 8-kb stretch downstream of the transposed segment not cut by several restriction endonucleases. The 5' borders of the two transposed segments are homologous and contain sequences present in many copies in the genome. A different repeated sequence has previously been found at the 3' edge of the transposed segment. The replicative transposition may, therefore, involve a unidirectional gene conversion initiated by base pairing between the edges of the transposed sequence and a single expression site elsewhere in the genome.

Preparation and in vitro translation of mRNA from Fasciola hepatica

Total RNA was extracted from mature and juvenile Fasciola hepatica by homogenizing in 5.0 M guanidine thiocyanate and centrifugation through a 5.7 M CsCl cushion. Yields of 2 mg/g and 1 mg/g wet weight starting material were obtained, respectively. Messenger RNA was separated from the bulk extracted RNA by binding to oligo(dT)-cellulose. About 25% of the extracted RNA bound in both adult and juvenile cases. This material was subsequently tested in a rabbit reticulocyte cell-free translation system. Up to a 12-fold stimulation of incorporation of [35S]methionine into trichloroacetic acid-precipitable material was observed over that where no message was added. When the in vitro translation products were analysed by autoradiography of SDS-polyacrylamide gradient gels, polypeptides ranging in apparent molecular weight from about 10,000 to 100,000 were observed. Several minor differences in the electrophoretic patterns obtained from juvenile and adult mRNA were observed.

Isolation of Trypanosoma brucei variant specific antigen mRNA by immunoprecipitation of polysomes

The mRNA encoding the variant specific antigen of Trypanosoma brucei has been prepared by immunoprecipitation of polysomes. Polysomes carrying the variant specific antigen account for approx. 3% of the total polysomes. The mRNA thus produced is active in the mRNA dependent rabbit reticulocyte lysate in vitro protein synthesis system and directs the synthesis of a polypeptide of 60 000 daltons which co-migrates both with 125I-labelled purified variant specific antigen and with antigen immunoprecipitated from reticulocyte lysate charged with total polyadenylated mRNA from the same clone. The mRNA is being used both to prepare cDNA clones and to prepare high specific radioactivity cDNA to be used to screen a gene bank for clones containing variant specific antigen coding sequences.

Purification and cell-free translation of mRNA coding for a variant specific antigen from Trypanosoma brucei gambiense

Messenger RNA (mRNA) coding for a variant specific surface antigen (VSA) from Trypanosoma brucei gambiense was isolated from total trypanosomal polyribosomes by indirect immunoprecipitation. An IgG fraction of antisera to purified VSA was obtained by ion exchange chromatography and Protein A-agarose affinity chromatography. These antibodies were then subjected to affinity chromatography on a VSA-agarose column to remove non-specific IgG. Polyribosomes from the same antigenic variant of T. b. gambiense were isolated from a cell lysate and those polysomes bearing nascent VSA were bound to the IgG by gentle mixing and the complexes formed were retrieved by precipitation with fixed Staphylococcus aureus cells. The VSA-specific mRNA was separated from these complexes by dissociation of the polysomes, deproteinization, and affinity chromatography on oligo(dT)-cellulose. The mRNA isolated in this way was shown to be undegraded, active in protein synthesis and homogeneous electrophoretically. The products of the cell-free translation of this mRNA were precipitable by specific IgG but not by antiserum to a heterologous VSA. The translation product was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel exclusion chromatography. The molecular weight of the mRNA was measured by electron microscopy, agarose and polyacrylamide gel electrophoresis. Enough highly purified mRNA can be isolated in this manner to be used for hybridization analysis of the VSA gene(s).

The isolation of plasmids containing DNA complementary to messenger RNA for variant surface glycoproteins of Trypanosoma brucei

We have isolated poly(A)+ RNA from four antigenic variants (117, 118, 121, 221) of one clone of Trypanosoma brucei. Translation of these poly(A)+ RNAs in a rabbit reticulocyte lysate gave rise to proteins that could be precipitated with antisera against homologous variant surface glycoprotein, the protein responsible for antigenic variation in trypanosomes. From the electrophoretic mobility of these in vitro products in sodium dodecyl sulphate (SDS) gels we infer that variant surface glycoproteins (VSGs) are made as pre-proteins, which require trimming to yield mature VSGs. The total translation products from the four poly(A)+ RNAs produced a complex set of bands on SDS gels, which only differed in the region where the variant pre-glycoproteins migrated. The only detectable variation in the messenger RNA populations of these variants is, therefore, in the messenger RNA for variant pre-glycoproteins. We have made duplex DNA copies of these poly(A)+ RNAs, linked the complementary DNA to plasmid pBR322 by GC tailing and cloned this recombinant DNA in Escherichia coli. Colony hybridization with complementary DNA made on poly(A)+ RNA showed that 7--10% of the colonies contained DNA that hybridized only with the homologous probe. Plasmid DNA was isolated from ten such colonies (two or three of each variant complementary DNA), bound to diazobenzyloxymethyl-cellulose (DBM) paper and used to select complementary messenger RNA from total poly(A)+ RNA by hybridization. In eight cases the RNA recovered from the filter gave variant pre-glycoprotein as the predominant product of in vitro translation. Poly(A)+ RNA from each of the variants only hydridized to the homologous complementary DNA in filter hybridizations. Each trypanosome variant, therefore, contains no detectable messenger RNAs for the three heterologous variant-specific glycoproteins tested. We conclude from this lack of cross-hybridization that antigenic diversity in trypanosomes, unlike antibody diversity in mammals, does not involve the linkage of a repertoire of genes for the variable N-terminal half to a single gene for the C-terminal half of the VSGs.

Lectin analysis of Trypanosoma congolense bloodstream trypomastigote and culture procyclic surface saccharides by agglutination and electron microscopic technics

Living, intact bloodstream trypomastigotes and culture procyclic forms of Trypanosoma congolense were tested for aggulination with the lectins concanavalin A (Con A), phytohemagglutinin P (PP), wheat germ agglutinin (WGA), soybean agglutinin (SBA), and fucose binding protein (FBP). Similar experiments were conducted with living bloodstream and culture forms treated with trypsin or dextranase. Parasites were incubated for 30 min at 25 C in various concentrations of each lectin, then examined for agglutination by dark-field microscopy. Control preparations consisted of parasites incubated alone or with 0.5 M of the specific competing sugar, with or without the corresponding lectin. Electron-microscopic localization of lectin binding sites on the surface of intact and dextranase-treated bloodstream and intact culture forms was accomplished with Con A, reacted with horseradish peroxidase (HRP) and then diaminobenzidine (DAB). In addition, FBP and SBA were coupled to HRP, then utilized for the localization of binding saccharides on the surface of bloodstream forms by the DAB technic. Similar studies were conducted with culture procyclics incubated with WGA-, SBA-, PP- or FBP-HRP conjugates and then reacted with DAB. Controls were utilized to confirm the sugar specificity of all positive reactions. Intact living bloodstream forms were agglutinated in a concentration-dependent manner with all the lectins tested. Agglutination levels were scored as Con A greater than FBP greater than WGA = PP = SBA. Sugars resembling alpha-D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and alpha-L-fucose are evidently present on the surface of the parasites. No agglutination was noted in any control preparations. Identical lectin-induced agglutinations were obtained with trypsin- or dextranase-treated bloodstream forms. Trypsin disrupted but did not entirely remove the surface coat of bloodstream forms, while dextranase did not alter the ultrastructure of the parasites. Con A-, SBA- and FBP-binding saccharides were distributed uniformly on the surface coat of intact bloodstream forms; a similar distribution of Con A receptors was noted also on the surface of dextranase-treated cells. No lectin-binding saccharides were visualized by electron microscopy on any control preparations. Intact, trypsin- or dextranase-treated, procyclics were agglutinated in a concentration-dependent fashion by Con A and WGA, but not by the other lectins tested. Control preparations did not agglutinate and the enzymes did not affect the ultrastructure of the parasites. Con A- and WGA-specifically binding saccharides were uniformly distributed on intact procyclics and control preparations were lectin-negative. Thus, T. congolense procyclics retained surface saccharides resembling alpha-D-mannose and N-acetyl-D-glucosamine but lost sugars resembling N-acetyl-D-galactosamine (or D-galactose) and alpha-L-fucose...

A characterization of mRNA activites and their sequence complexities in Trypanosoma brucei: partial purification and properties of the VSSA mRNA

Polyadenylated RNA isolated from a clone of Trypanosoma brucei was shown to direct the synthesis of a variety of polypeptides in a cell-free system. A predominant 58,000 dalton polypeptide was immunoprecipitated with antisera to the T. brucei variant specific surface antigen (VSSA). The mRNA that directed the synthesis of the VSSA was 2.0 kilobases (kb) long as measured by polyacrylamide gel electrophoresis in 98% formamide. Complementary DNA was prepared with avian myeloblastosis virus reverse transcriptase and the nucleotide sequence complexities of the total polysomal poly(A)+RNA and a gel purified VSSA mRNA were measured. 20% of the total cellular poly(A)+RNA contained abundant sequences with an apparent complexity of 9.6 kb; 42% of the purified VSSA mRNA contained abundant sequences with a complexity of 7.2 kb. Complementary DNA synthesized from gel purified VSSA mRNA was hybridized to total cellular poly(A)+RNA isolated from an unrelated T. brucei clone expressing a different variant antigen. A portion of the low complexity RNA sequence component was absent in the heterologous mRNA population but the same plateau of hybridization was achieved (93%). The abundance of some of the low complexity mRNAs appears to be T. brucei clone specific.