The significance and effect of tandem repeats within the Mycobacterium tuberculosis leuA gene on alpha-isopropylmalate synthase

The 57-bp tandem repeats located in the Mycobacterium tuberculosis leuA gene code for the alpha-isopropylmalate synthase (alpha-IPMS). It is unique to this pathogen. It was previously demonstrated that the leuA-coding sequence Rv3710, containing the tandem repeats, can be translated to an active alpha-IPMS. The objective of the present study was to investigate the significance and effect of the two 57-bp tandem repeats upon gene expression and the general properties of alpha-IPMS. The putative M. tuberculosis H37Rv leuA gene with and without the tandem repeats was cloned by PCR and expressed in an Escherichia coli host. The enzyme product was studied for general properties, comparing that from a native leuA gene containing two repeats and that from the 57-bp tandem repeats deletion mutant. Upon deletion of the two 57-bp tandem repeats, the expression level of leuA from M. tuberculosis H37Rv was comparable with that of the native form. The general properties of the two types of enzymes were similar. They were both functional with the same range of optimal temperature and optimal pH for activity and with similar enzyme stability. Deletion of the repeats had no detectable effect on leuA expression level or the general properties of the enzyme product.     

Gametocyte clearance in uncomplicated and severe Plasmodium falciparum malaria after artesunate-mefloquine treatment in Thailand

Artemisinin-based combination therapy (ACT) is currently promoted as a strategy for treating both uncomplicated and severe falciparum malaria, targeting asexual blood-stage Plasmodium falciparum parasites. However, the effect of ACT on sexual-stage parasites remains controversial. To determine the clearance of sexual-stage P. falciparum parasites from 342 uncomplicated, and 217 severe, adult malaria cases, we reviewed and followed peripheral blood sexual-stage parasites for 4 wk after starting ACT. All patients presented with both asexual and sexual stage parasites on admission, and were treated with artesunate-mefloquine as the standard regimen. The results showed that all patients were asymptomatic and negative for asexual forms before discharge from hospital. The percentages of uncomplicated malaria patients positive for gametocytes on days 3, 7, 14, 21, and 28 were 41.5, 13.1, 3.8, 2.0, and 2.0%, while the percentages of gametocyte positive severe malaria patients on days 3, 7, 14, 21, and 28 were 33.6, 8.2, 2.7, 0.9, and 0.9%, respectively. Although all patients were negative for asexual parasites by day 7 after completion of the artesunate-mefloquine course, gametocytemia persisted in some patients. Thus, a gametocytocidal drug, e.g., primaquine, may be useful in combination with an artesunate-mefloquine regimen to clear gametocytes, so blocking transmission more effectively than artesunate alone, in malaria transmission areas.     

The significance and effect of tandem repeats within the Mycobacterium tuberculosis leuA gene on α-isopropylmalate synthase

The 57-bp tandem repeats located in the Mycobacterium tuberculosis leuA gene code for the α-isopropylmalate synthase (α-IPMS). It is unique to this pathogen. It was previously demonstrated that the leuA -coding sequence Rv3710, containing the tandem repeats, can be translated to an active α-IPMS. The objective of the present study was to investigate the significance and effect of the two 57-bp tandem repeats upon gene expression and the general properties of α-IPMS. The putative M. tuberculosis H37Rv leuA gene with and without the tandem repeats was cloned by PCR and expressed in an Escherichia coli host. The enzyme product was studied for general properties, comparing that from a native leuA gene containing two repeats and that from the 57-bp tandem repeats deletion mutant. Upon deletion of the two 57-bp tandem repeats, the expression level of leuA from M. tuberculosis H37Rv was comparable with that of the native form. The general properties of the two types of enzymes were similar. They were both functional with the same range of optimal temperature and optimal pH for activity and with similar enzyme stability. Deletion of the repeats had no detectable effect on leuA expression level or the general properties of the enzyme product.