Variable number of tandem repeat sequences act as regulatory elements in Mycobacterium tuberculosis

VNTR (variable number of tandem repeats) has been used extensively for Mycobacterium tuberculosis strain discrimination. In contrast, their biological roles have been rarely investigated. We, herewith, studied whether two VNTR could promote expression of a downstream reporter gene, gfp. The VNTR loci, VNTR0960c and VNTR4052, reside upstream of the translational start sites of Rv0861c (helicase gene, ercc3) and Rv3610c (ftsH), respectively. Both are highly polymorphic among clinical strains of M. tuberculosis. DNA fragments containing various numbers of the repeat units were amplified and inserted upstream of the gfp gene and transformed into M. smegmatis mc2155 and M. tuberculosis H37Ra. The levels of fluorescence were determined by microplate fluorometry and flow cytometry. It was found that VNTR0960c could promote the expression of gfp while VNTR4052 alone could not. However, VNTR4052 was needed for complementing the promoter activity of the downstream sequence. The effects were discernible in M. tuberculosis, even though only the incomplete copy of the repeat was present. The addition of a complete copy of the repeat augmented the promoter activity. The presence of more copies of the repeat had minimal effects or even decreased the expressions. Significance of the effects on the cellular metabolisms of M. tuberculosis warrants further studies.