Specificity of the bacteriophage lambda N gene product (p N): Nut sequences are necessary and sufficient for antitermination by p N

Abstract

We have cloned the nut R site together with the t R1 site of bacteriophage lambda in the E. coli galactose operon to examine whether the λ promoter sequences P R and P L are involved in the recognition specificity of the λ N gene product (p N). We first constructed a derivative of plasmid pBR322 in which the expression of the tetracycline genes ( tet) is controlled by the gal promoter ( P gal). This new plasmid contains a unique Hind III site between P gal and tet into which the nut R and t R1 sites were introduced. The order of the relevant genetic markers in this second plasmid is P gal- nut R- t R1-tet. Cells transformed with this plasmid express tet only if p N is provided and if the plasmid contains an intact gal promoter. Our data suggest that transcription which originates at P gal is modified by pN at nut R, enabling it to pass through t R1 into tet. We conclude that promoters do not play a specific role in p N recognition and that nut sequences are both necessary and sufficient for p N action.