Molecular anatomy of the β′ subunit of the E. coli RNA polymerase: Identification of regions involved in polymerase assembly

Abstract

Background: The E. coli RNA polymerase is a multisubunit enzyme, which is present in two different forms: the catalytic competent core enzyme (α2ββ′) and the promoter selective holoenzyme (α2ββ′σ). Correct assembly of individual subunits into core or holoenzyme is essential for the function of this enzyme. Results: Mutant β′ proteins truncated near the centre or at the C-terminus were able to form stable core enzyme-like complexes under reconstitution conditions. Mutant β′ proteins lacking the region between amino acids 201-477 failed to form holoenzyme complexes while retaining the ability to form core enzyme complexes. Furthermore, free β′ subunit interacted with free σ subunit to form a stable β′σ subassembly. Removal of amino acids 201-477 from the β′ subunit strongly interfered with this interaction. Conclusion: Our results suggest that the N-terminal region of the β′ subunit is involved in the assembly of core enzyme. The region between amino acids 201 and 477 on β′ may be directly or indirectly involved in the interaction between the β′ subunit and the σ subunit. © Blackwell Science Limited.