Conditionally lethal nusAts mutation of Escherichia coli reduces transcription termination but does not affect antitermination of bacteriophage lambda.

Termination of transcription at bacteriophage lambda terminators as well as at the Escherichia coli trp a attenuator was examined in the conditionally lethal mutant (nusAts11) defective in the NusA protein of E. coli. Experiments using terminator-assay lambda vectors revealed that the efficiency of termination at both rho-dependent (lambda tL1) and rho-independent (lambda tL2 and trp a) terminators decreases in the mutant. The mutation does not block lambda phage growth at either permissive or nonpermissive temperatures, nor does it affect the lambda Q protein antitermination activity at the t6s terminator. These results indicate that NusA is required for transcription termination, and that lambda N and Q-mediated antitermination may not require the NusA protein function in the nusAts11 mutant.