[lambda] N antitermination system: Functional analysis of phage interactions with the host NusA protein

Abstract

Coliphage [lambda] gene expression is regulated temporally by systems of termination and antitermination of transcription. The [lambda]-encoded N protein (pN) acting with host factors (Nus) at sites (nut) located downstream from early promoters is the first of these systems to operate during phage development. We report observations on some of the components of this complex system that, in part, address the way in which these elements interact to render RNA polymerase termination-resistant. (1) The isolation of a conditionally lethal cold-sensitive nusA mutation demonstrates that NusA is essential for bacterial growth. (2) The effect on [lambda] growth in a host in which the Salmonella NusA protein is overproduced suggests that NusA is essential for N-mediated antitermination in phage [lambda]. (3) A truncated NusA product, representing only the amino two-thirds of the native protein, is active for both bacterial growth and pN action, indicating that the carboxy end of the molecule may not be a functionally important region. (4) [lambda] pN can function with the heterologous nut region from Salmonella typhimurium phage P22 when [lambda] pN is overproduced, demonstrating that [lambda] pN can function with the nut regions of other lambdoid phages. (5) A single base-pair change in the [lambda] nutR boxA sequence that was selected to permit a [lambda] derivative to utilize the Salmonella NusA protein restores [lambda] growth in the Escherichia coli nusA1 host.