Tag:λN22 represents an arginine-rich 22 amino acid peptide derived from the Enterobacteriophage lambda N protein that binds specifically to Tag:BoxB, a 15bp minimal RNA hairpin (PMID:17603490). Tag:BoxB and Tag:λN22 thus form a binary RNA-protein interacting pair which are typically used to either monitor or alter the localization of an mRNA of a gene of interest, depending on what other sequence the Tag:λN22 component is fused to. For example, if a transgene or modified endogenous locus in which the Tag:λN22 protein is fused to a fluorescent protein is combined with a second transgene or modified endogenous locus encoding an mRNA of interest tagged with the Tag:BoxB stem loop, the localization of this tagged mRNA can be followed in vivo. Conversely, if the Tag:λN22 protein is fused to sequence that targets it to a particular subcellular location, it be used to target an mRNA of interest tagged with the Tag:BoxB stem loop to that location, so that the effect of altering the location of the tagged mRNA can be studied.