The present invention is directed to the discovery of a novel family of enzymes designated herein as mRNA interferases that exhibit endoribonuclease activity. The novel finding of the present inventors, therefore, presents new applications for which mRNA interferase nucleic and amino acid sequences, and compositions thereof may be used to advantage. The invention also encompasses screening methods to identify compounds/agents capable of modulating mRNA interferase activity and methods for using such compounds/agents. Also provided is a kit comprising mRNA interferase nucleic and/or amino acid sequences, mRNA interferase activity compatible buffers, and instruction materials.