In higher eukaryotes, DNA polymerase (pol) ␤ resides in the nucleus and participates primarily in DNA repair. The DNA polymerase ␤ from the trypanosomatid Crithidia fasciculata, however, was the first mitochondrial enzyme of this type described. Upon searching the nearly completed genome data base of the related parasite Trypanosoma brucei, we discovered genes for two pol ␤-like proteins. One is ϳ70% identical to the C. fasciculata pol ␤ and is likely the homolog of this enzyme. The other, although ϳ30% identical within the polymerase region, has unusual structural features including a short C-terminal tail and a long N-terminal extension rich in prolines, alanines, and lysines. Both proteins, when expressed recombinantly, are active as DNA polymerases and deoxyribose phosphate lyases, but their polymerase activity optima differ with respect to pH and KCl and MgCl 2 concentrations. Remarkably, green fluorescent protein fusion proteins and immunofluorescence demonstrate that both are mitochondrial, but their locations with respect to the mitochondrial DNA (kinetoplast DNA network) in this organism are strikingly different.

Human T-cell leukemia virus I (HTLV-I) is a deltaretrovirus that is the causative agent of adult T-cell leukemia and the neurological disorder HTLV-I-associated myelopathy/tropical spastic paraparesis. Currently, no effective antiretroviral treatment options are available to restrict the development of diseases associated with the virus. In this work, we investigated the activity of pokeweed antiviral protein (PAP) on HTLV-I, when expressed from a proviral clone in 293T cells or in an HTLV-I immortalized cell line. PAP is a plant-derived N-glycosidase that exhibits antiviral activity against a number of viruses; however, its mode of action has not been clearly defined. Here, we describe the mechanism by which PAP inhibited production of HTLV-I. We show that PAP depurinated nucleotides within the gag open reading frame and suppressed the synthesis of viral proteins in part by decreasing the translational efficiency of HTLV-I gag/pol mRNA. Observed reduction in levels of viral mRNAs were not due to enhanced degradation; rather, decreased amounts of viral transactivator protein, Tax, led to feed-back inhibition of transcription from the viral promoter. Therefore, PAP efficiently suppressed HTLV-I gene expression at both translational and transcriptional levels, resulting in substantially diminished virus production. Significantly, no changes in viability or rates of cellular transcription or translation were observed in cells expressing PAP, indicating that this protein was not toxic. Antiviral activity, together with the absence of cytotoxicity, supports further investigation of this enzyme as a novel therapeutic agent against the progression of HTLV-I infection.

Human T-cell leukemia virus type 1 (HTLV-1) basic leucine zipper factor (HBZ) is transcribed from the antisense genomic DNA strand and functions differently in its RNA and protein forms. To distinguish between the roles of hbz mRNA and HBZ protein, we generated mutants in a proviral clone that specifically disrupt the hbz gene product. A proviral clone with a splice acceptor mutation that disrupts expression of the predominant hbz mRNA resulted in lower levels of tax mRNA. Heterologous hbz expression restored Tax activity in cells expressing this mutant clone. In contrast, proviral mutants that disrupt HBZ protein did not affect levels of tax mRNA. Expression of hbz resulted in lower levels of p30II mRNA. Mutation of p30II overcame the effects of the splice acceptor mutation of hbz, and restored tax expression. Thus, there is a complex interplay of viral regulatory proteins controlling levels of HTLV-1 gene expression.

Parosteal osteosarcomas are rare, low-grade juxtacortical variant of osteosarcoma, especially in the jaws, representing 1.6% of all bony malignant tumours and upto 5% of all osteosarcomas. Only 12 cases of intraoral parosteal osteosarcomas have been reported in the English literature. In the jaws males are more commonly affected with peak occurrence at 39 years and nearly equal site predilection for maxilla and mandible. Radiographically, parosteal osteosarcomas are radiodense, lobulated masses with a broad stalk to the cortex of the bone with no periosteal reaction and medullary invasion. Microscopically, shows well-differentiated tumor with minimum atypia and rare mitotic figures separating trabeculae of woven bone. Unlike classical and periosteal osteosarcoma, it is considered to have a good prognosis. A case report of this rare entity in 22-year-old female patient with bony hard, painless swelling of 9 months duration in maxillary premolar-molar region is presented. The need for differential diagnostic approach is emphasized from other seemingly benign clinical entities.