RNA Imaging with RNase-Inactivated Csy4 in Plants and Filamentous Fungi.

Subcellular localizations of RNAs can be imaged in vivo with genetically encoded reporters consisting of a sequence-specific RNA-binding protein (RBP) fused to a fluorescent protein. Several such reporter systems have been described based on RBPs that recognize RNA stem-loops. Here we describe RNA tagging for imaging with an inactive mutant of the bacterial endonuclease Csy4, which has a significantly higher affinity for its cognate stem-loop than alternative systems. This property allows for sensitive imaging with only few tandem copies of the target stem-loop inserted into the RNA of interest.