AN RNA-POLYMERASE ALPHA-SUBUNIT MUTANT IMPAIRS N-DEPENDENT TRANSCRIPTIONAL ANTITERMINATION IN ESCHERICHIA-COLI

We show that the rpoA341 mutation in the gene encoding the cu subunit of Escherichia coli RNA polymerase results in a decreased level of tra nscripts originating from the lytic promoters p(L) and p(R) of infecti ng lambda phage. However, using lacZ fusions we demonstrate that initi ation of transcription from both p(L) and p(R) is not impaired in the rpoA341 host. Rather, it is the level of the longer, antiterminated p( L)- and p(R)-derived transcripts which is altered: the activity of P-g alactosidase in bacteria harbouring a source of N and a p(L)-nutL-t(L1 )-t(l)-lacZ or P-R-nutR-t(R1)-lacZ fusion is considerably lower in the rpoA341 mutant relative to the rpoA(+) strain. In the absence of the antiterminator protein N no difference is observed in the level of lon ger p(R)-derived transcripts between wild-type (rpoA(+)) and mutant (r poA341) hosts. Although synthesis of N appears to be similar in both p hage-infected rpoA(+) and rpoA341 cells, overexpression of the N gene leads to restoration of wild-type levels of the longer p(L)- and p(R)- derived transcripts in the mutant host. While this mutation does not a ppear to affect vegetative phage growth in nus(+) backgrounds, in comb ination with certain nus mutations it retards lytic development. There fore, we conclude that the rpoA341 mutation specifically interferes wi th the function of the N-antitermination complex, suggesting that the C-terminal domain of the RNA polymerase alpha subunit may play an impo rtant role in N-dependent transcriptional antitermination.