Figure 1.

Phylogenetic relationships between members of the σ⁷⁰ family of sigma factors from four diverse bacteria: E. coli (E); Caulobacter cresentus (CC or C); B. subtilis (B); and Mycobacterium tuberculosis (M). For C. cresentus, gene numbers from the annotated genome sequence are given. Note that the primary and related factors comprise groups 1 and 2, the group 3 σ factors are divided into functionally related groups (sporulation, flagellar biosynthesis, general stress and heat shock), and the divergent ECF factors comprise group 4. Particularly striking is the distance between the ECF subfamily and other members of the σ⁷⁰ family, as well as divergence within the ECF subfamily itself. The unrooted tree was constructed using the Phylip programs PROTDIST and NEIGHBOUR from a multiple amino-acid sequence alignment made by the program ClustalW. Only conserved regions 2 and 4 were included in the alignments.