Abstract: Provided herein are proteins having A-specific RNase activity. A protein having A-specific RNAse activity is referred to herein as a Csx1 protein. A Csx1 protein is an endoribonuclease, and has the activity of cleaving the phosphodiester bond in a single strand of a target RNA molecule on the 3? (downstream) side of an adenosine base to result in a first cleavage product having a 5? hydroxyl group and a second cleavage product having a 2?,3?-cyclic phosphate at the 3? end. Also provided herein are methods for using a Csx1 protein. In one embodiment, the method includes incubating a sample that includes an isolated Csx1 protein and a target RNA molecule under suitable conditions for cleavage of the target RNA molecule. Also provided is a genetically modified microbe that includes an exogenous polynucleotide including a nucleotide sequence encoding a Csx1 protein, and a method for making Cxsl protein.