FIG 2.

Graphical diagram representing the regulatory role of G-quadruplex sequences in replication and transcription (by either inhibiting or promoting expression). The presence of secondary structure G4 DNA stalls DNA replication in many bacterial species, while the destabilization of G4 DNA in the presence of helicase enzymes Rec Q, Rec A, and UvrD (studied in E. coli) and UvrD1, UvrD2, and DinG (investigated in M. tuberculosis) and topoisomerase DraTopoIB of M. tuberculosis results into the resumption of stalled DNA replication. The transcriptional regulation of many genes is observed to be either continued or hindered by G4 DNA in many bacteria. With the use of certain ligands such as NMM and TMPyP4, G4 DNA is stabilized and transcription of genes such as recA, recO, recF, recR, and recQ in D. radiodurans, espK, espB, and cyp51 in M. tuberculosis, and nasT in P. denitrificans is observed to be obstructed.