Dynamic of IS6110 transposase, transframe protein responsible for IS6110 element transposition in Mycobacterium tuberculosis strains

Transposition of IS6110, the Mycobacterium tuberculosis Complex specific insertion sequence, is mediated by the complex open reading frame AB (orfAB) transframe protein or transposase. Transposase has the crucial role to ensure IS6110 transposition process. A single transposase proteine can control the integration of many IS6110 copies at the same time. In this work we investigated the dynamic and the evolutionary trends of IS6110 transposase coding gene isolated from various hosts. We had subjected these sequences to several statistical tests combined with programming package analysis. Our findings showed that IS6110 transposase-encoding orfAB is subjected to purifying selection with low genetic variability rate, as demonstrated by its significantly negative Tajima’s D statistics as well as by LRT analysis and models comparison. Even some codons tended to be positively selected, global p-value didn’t reach reliable inference (ω > 1) of significant positive selection at these positions; so statistically they were not significant. In conclusion, our findings demonstrated that IS6110 transposase-encoding orfAB evolved essentially by point mutations under purifying selection acting against deleterious mutations, thus leading to an excess of low-frequency variants and purging disadvantageous non synonymous changes.