Sigma factors are components of the RNA polymerase complex that are responsible for binding to the RNA polymerase complex, promoter recognition and separating DNA strands. The number of sigma factors is extremely diverse between bacteria, ranging from three in Helicobacter pylori to 63 in Streptomyces coelicolor. M. tuberculosis possesses 13 sigma factors, 10 of which are from the ECF sub-family, enabling this bacterium to cope with various environmental conditions