sfrA and sfrB products of Escherichia coli K-12 are transcriptional control factors.

The mechanisms whereby mutations in Escherichia coli K-12 genes sfrA and sfrB reduce expression of the transfer functions of sex factor F have been examined by assaying the levels of tra messenger ribonucleic acid and of tra proteins. The sfrA product was necessary for efficient transcription of the control gene traJ and, directly or indirectly, for transcription of the traY leads to Z operon. In the absence of sfrA, reduced levels of the traJ and traT proteins were observed in the outer membrane. The sfrB product was needed to prevent premature transcription at one or more rho-dependent termination sites. sfrB mutations also reduced synthesis of full-length lipopolysaccharide molecules, of several chromosomally determined outer membrane proteins, and of functional flagella. Thus, the sfrB product may act as an antiterminator in transcription of several operons encording cell envelope components.