C2 and infection: While many examples of loss of fitness in mouse infection were observed for DUBs and other ubiquitination system mutants studied (S4 Table), loss of fitness phenotypes were less common for other peptidase mutants in the screen, including members of the calpain (C2), SUMO-specific peptidase (C97) and D-alanyl-glycyl endopeptidase (C51) families [26].