A review.To extend the structural coverage of proteins with unknown functions, we targeted a novel protein family (Pfam accession number PFO8807, DUF1798)1 for which we proposed and determined the structures of two representative members.The MW1337R gene of Staphylococcus aureus subsp. aureus Rosenbach encodes a protein with a mol. weight of 13.8 kDa (residues 1-116) and a calculated isoelec. point of 5.15.The lin2004 gene of the nonspore-forming bacterium Listeria innocua Clip11262 encodes a protein with a mol. weight of 14.6 kDa (residues 1-121) and a calculated isoelec. point of 5.45.MW1337R and lin2004, as well as their homologs, which, so far, have been found only in Bacillus, Staphylococcus, Listeria, and related genera (Geobacillus, Exiguobacterium, and Oceanobacillus), have unknown functions and are annotated as hypothetical proteins.Here, we report the crystal structures of MW1337R and lin2004, which were determined using the semiautomated, high-throughput pipeline of the Joint Center for Structural Genomics (JCSG), part of the National Institute of General Medical Sciences' Protein Structure Initiative.