Molecular anatomy of the beta' subunit of the E. coli RNA polymerase: identification of regions involved in polymerase assembly.

BACKGROUND: The E. coli RNA polymerase is a multisubunit enzyme, which is present in two different forms: the catalytic competent core enzyme (alpha2beta beta') and the promoter selective holoenzyme (alpha2beta beta' sigma). Correct assembly of individual subunits into core or holoenzyme is essential for the function of this enzyme.
RESULTS: Mutant beta' proteins truncated near the centre or at the C-terminus were able to form stable core enzyme-like complexes under reconstitution conditions. Mutant beta' 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 beta' subunit interacted with free sigma subunit to form a stable beta' sigma subassembly. Removal of amino acids 201-477 from the beta' subunit strongly interfered with this interaction.
CONCLUSION: Our results suggest that the N-terminal region of the beta' subunit is involved in the assembly of core enzyme. The region between amino acids 201 and 477 on beta' may be directly or indirectly involved in the interaction between the beta' subunit and the sigma subunit.