Two separable functional domains in the σ‐subunit of RNA polymerase in Bacillus subtilis?

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Abstract
The σ-subunit of RNA polymerase is responsible for promoter recognition in prokaryotes [(1969) Nature 221, 43–46]. Alterations in the σ-subunit are thought to be involved in controlling ‘global’ changes in gene expression, such as those involved in differentiation in the spore-forming bacterium Bacillus subtilis [(1981) Cell 25, 582–584]. Stragier et al. [(1985) FEBS Lett. 195, 3–11] have proposed that σ-factors are composed of two domains: a C-terminal domain involved in promoter recognition and an N-terminal domain involved in interactions with RNA polymerase. We have sequenced another developmental gene from B. subtilis , spoIIIC , and the strong homology of its predicted product suggests that it too may be a σ-factor. However, the spoIIIC product is small and lacks completely the conserved N-terminal domain of the σ-subunits. I propose that the product of the spoIIIC gene may carry out the DNA-recognition functions of a σ-factor but that it probably requires an auxiliary factor to interact with core RNA polymerase.