YdaL is a small endonuclease with homology to the C-terminal domain found in the endonuclease MutS2, but not found in the related mismatch repair protein MutS. The biological role of this endonuclease is not yet known. As one of two Small MutS2-Related proteins in E. coli, This protein was designated SmrA by Gui, et al. (PMID:21276852). The term SMR is much better known for describing a large family of Small Multidrug Resistance (SMR) efflux transporters, but in that context is used with three capital letters.