The procyclic acidic repetitive protein (parp) genes of Trypanosoma brucei encode a small family of abundant surface proteins whose expression is restricted to the procycfic form of the parasite. They are found at two unlinked loci, parpA and parpB; transcription of both loci is developmentally regulated. The region of homology upstream of the A and B parp genes is only 640 base pairs long and may contain sequences responsible for transcriptional initiation and regulation. Transcription upstream of this putative promoter region is not developmentally regulated and is much less active than that of the parp genes; the polymerase responsible is inhibited by a-amanitin, whereas that transcribing the parp genes is not. Transcription of the parp genes is strongly stimulated by low levels of UV irradiation. The putative parp promoter, when placed upstream of the chloramphenicol acetyltransferase gene, is sufficient to cause production of chloramphenicol acetyltransferase in a T. brucei DNA transformation assay. Taken together, these results suggest that a promoter for an a-amanitin-resistant RNA polymerase lies less than 600 nucleotides upstream of the parp genes.

The use of a highly specific radioimmunoassay and of HPLC permitted us to confirm the occurrence of 2′–5′ oligoadenylates [px(A2′p5′)nA] in several strains of Escherichia coli. Cellular concentrations of 2′–5′ oligoadenylates ranged from 50 nM to 300 nM. The mixture of 2′–5′ oligoadenylates consisted primarily of pppA2′p5′A, pA2′p5′A, A2′p5′Ap and A2′p5′A under normal conditions of growth. None of them activated R Nase L. Infection of the bacteria with the single‐stranded DNA phage M13 or induction of a heat‐inducible, non‐lytic mutant of phage λ led to a significant increase in the total pool of 2′–5′ oligoadenylates, paralleling the progressive inhibition of growth. Likewise, the inhibition of protein synthesis with chloramphenicol stimulated the accumulation of 2′–5′ oligoadenylates. Furthermore, the inhibition of bacterial growth by either phage or by chloramphenicol brought about a change in the composition of the 2′–5′ oligoadenylate pool; 5′‐phosphorylated 2′–5′ oligoadenylates accumulated and became the major components. The findings indicate a parallelism between the effects of viral infection on the synthesis of 2′–5′ oligoadenylates in eukaryotes and similar effects subsequent to phage growth in the bacterium E. coli.

No abstract

The procyclic acidic repetitive protein (parp) genes of Trypanosoma brucei encode a small family of abundant surface proteins whose expression is restricted to the procyclic form of the parasite. They are found at two unlinked loci, parpA and parpB; transcription of both loci is developmentally regulated. The region of homology upstream of the A and B parp genes is only 640 base pairs long and may contain sequences responsible for transcriptional initiation and regulation. Transcription upstream of this putative promoter region is not developmentally regulated and is much less active than that of the parp genes; the polymerase responsible is inhibited by alpha-amanitin, whereas that transcribing the parp genes is not. Transcription of the parp genes is strongly stimulated by low levels of UV irradiation. The putative parp promoter, when placed upstream of the chloramphenicol acetyltransferase gene, is sufficient to cause production of chloramphenicol acetyltransferase in a T. brucei DNA transformation assay. Taken together, these results suggest that a promoter for an alpha-amanitin-resistant RNA polymerase lies less than 600 nucleotides upstream of the parp genes.