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Pleiotropic effects of the rpoC10 mutation affecting the RNA polymerase β′ subunit of Escherichia coli on factor‐dependent transcription termination and antitermination

Escherichia coli RNA polymerase is composed of four different subunits, 2α, β, β′ and σ;. Among these subunits, the role of β′ is poorly understood. The rpoC10 mutation affecting β′ has been isolated as a suppressor mutation of the temperature‐sensitive nusA11 mutant. DNA sequence analysis revealed that the rpoC10 mutant is a substitution of Lys for Glu‐402. This increased positive charge appears to compensate for the increased negative charge present in the nusA11 protein (Asp for Gly‐181). In vivo measurements of reporter gene expression have revealed that rpoC10 restores ρ‐dependent termination but fails to restore ρ‐independent termination in nusA.11 Moreover, the rpoC10 mutation, in combination with any nusA mutation, inhibited λ Q‐mediated antitermination without affecting N antitermination and severely restricted λ phage development. The inhibition of Q function and λ growth could be compensated for by overproducing Q. These results suggest that the RNA polymerase β′ subunit plays a crucial rote in factor‐dependent transcription termination and antitermination.