REH2C Helicase and GRBC Subcomplexes May Base Pair through mRNA and Small Guide RNA in Kinetoplastid Editosomes.

Mitochondrial mRNAs in Trypanosoma brucei undergo extensive insertion and deletion of uridylates that are catalyzed by the RNA editing core complex (RECC) and directed by hundreds of small guide RNAs (gRNAs) that base pair with mRNA. RECC is largely RNA-free, and accessory mitochondrial RNA-binding complex 1 (MRB1) variants serve as scaffolds for the assembly of mRNA-gRNA hybrids and RECC. However, the molecular steps that create higher-order holoenzymes ("editosomes") are unknown. Previously, we identified an RNA editing helicase 2-associated subcomplex (REH2C) and showed that REH2 binds RNA. Here we showed that REH2C is an mRNA-associated ribonucleoprotein (mRNP) subcomplex with editing substrates, intermediates, and products. We isolated this mRNP from mitochondria lacking gRNA-bound RNP (gRNP) subcomplexes and identified REH2-associated cofactors 1 and 2 ((H2)F1 and (H2)F2). (H2)F1 is an octa-zinc finger protein required for mRNP-gRNP docking, pre-mRNA and RECC loading, and RNP formation with a short synthetic RNA duplex. REH2 and other eukaryotic DEAH/RHA-type helicases share a conserved regulatory C-terminal domain cluster that includes an oligonucleotide-binding fold. Recombinant REH2 and (H2)F1 constructs associate in a purified complex in vitro. We propose a model of stepwise editosome assembly that entails controlled docking of mRNP and gRNP modules via specific base pairing between their respective mRNA and gRNA cargo and regulatory REH2 and (H2)F1 subunits of the novel mRNP that may control specificity checkpoints in the editing pathway.

Bovine leukosis. IV. Trypanosomiasis, lymphocytosis and DNA synthesis.

The possible influence of natural trypanosome infection on lymphocytosis and DNA synthesizing lymphocyte counts in peripheral blood was determined on 220 cows from two leukosis herds and 25 cows from leukosis free control herd. Trypanosome incidences were determined during summers of 1969 and 1970 by inoculating whole blood onto blood agar slants and incubating at room temperature. Incidence of trypanosomiasis in cattle was found to be variable, possibly due to factors affecting the primary isolation of Trypanosoma theileri. A small trypanosome resembling Trypanosoma uniforme was found occasionally as a concomitant infection with T. theileri. Trypanosomiasis occurred with equal frequency in the animals of the leukosis and the control herds. No correlations were noted between trypanosomiasis, lymphocytosis and DNA synthesizing lymphocytes in peripheral circulation.

The composition of the Trypanosoma brucei subgroup in nonhuman reservoirs in the Lambwe Valley, Kenya, with particular reference to the distribution of T. rhodesiense.

Identification by means of the blood incubation infectivity test (BIIT) of 159 Trypanosoma brucei subgroup strains recently isolated from non-human hosts in the Lambwe Valley, Kenya, has defined the distribution in these hosts of both T. brucei and T. rhodesiense in an endemic sleeping sickness area. The presence of a small third group strongly suggestive of a population intermediate between these two species has also been revealed for the first time.Repeated testing of a number of these strains has shown marked consistency in the results. Strains identified by the BIIT as T. rhodesiense have been isolated for the first time from a reedbuck and a sheep. There appears to be direct relationship between the local prevalence rates of T. rhodesiense in non-human reservoirs and the incidence of sleeping sickness in man.

The isolation of trypanosomes from cattle in Ontario.

A method for the recovery by blood culture of a T. theilieri-like flagellate from cattle is described. In Ontario, 54% of 156 cows in 15 herds were found to have parasitemia.