The present disclosure provides variant Csy4 endoribonucleases, nucleic acids encoding the variant Csy4 endoribonucleases, and host cells genetically modified with the nucleic acids. The variant Csy4 endoribonucleases find use in a variety of applications, which are also provided. The present disclosure also provides methods of detecting a specific sequence in a target polyribonucleotide; and methods of regulating production of a target RNA in a eukaryotic cell.