Cloning, characterisation and phylogenetic analysis of the sigA (sigma) 70 factor gene sequence from the actinomycete Frankia

The (sigma)70 family of transcriptional factors is essential for bacterial life. Members of this family have been duplicated through evolution and have evolved and specialized for all sorts of physiological responses. Here, we have performed the first analysis of this gene family in Frankia. PCR was used to amplify Frankia (sigma)70 factors (essential for growth), and was thus named SigA. Early duplication events in this radiation led to the presence of several paralogs of primary-like (sigma)70 factors among the actinomycetes. These paralogous lineages could be divided into at least three well-resolved clusters: (A) a HrdA lineage found among Streptomyces; (B) a MysB-SigB lineage found among Mycobacterium and Brevibacterium, and (C) a MysAHrdB lineage widespread among the actinomycetes. Frankia SigA represents a distinct lineage in this radiation. Blot analysis of digested Frankia ACN14a total DNA showed sigA to be in a single copy.