This is a supplemental equipment request to the project R01GM111917 in response to NOT-GM-24-021 to purchase a Biacore™ X100 system from Cytiva. This unique piece of equipment takes advantage of the state-of-the-art technology (surface plasmon resonance) to monitor protein-RNA interactions within a protein complex consisting of eight monomeric subunits, which is capable of non-templated RNA tailing in vitro. We will be able to perform RNA binding assays and to determine whether the known inhibitors of reverse transcriptases would also affect non-templated tailing by the studied group of reverse transcriptase-like enzymes.