Antitermination in lambda is induced by two quite distinct mechanisms. The first is the result of interaction between lambda N protein and its targets in the early phage transcripts, and the second is the result of an interaction between the lambda Q protein and its target in the late phage promoter. We describe the N mechanism first. Lambda N, a small basic protein of the arginine-rich motif (ARM) family of RNA binding proteins, binds to a 15-nucleotide (nt) stem-loop called BOXB. (We will capitalize the names of sites in RNA and italicize the names of the corresponding DNA sequences; e.g., BOXB and "boxB".) "boxB" is found twice in the lambda chromosome, once in each of the two early operons. It is close to the start point of the PL operon transcript and just downstream of the first translated gene of the PR operon. Neither the distance between the transcription start site and "boxB", nor the nature of the promoter (at least in the case of sigma-70-dependent promoters), nor the nature of the terminator is relevant to N action. Although the "boxB" sequence is not well conserved in other bacteriophages of the lambda family, most of these phages encode proteins that are analogous to lambda N and have sequences capable of forming BOXB-like structures in their PL and PR operons. In some cases, it has been shown that these structures are recognized by the cognate N analogs. It is believed that this accounts for the phage specificity of N-mediated antitermination.