Domain composition of known USP proteins. In this figure, USP denotes the universal stress protein domain, CBS is the cystathionine beta synthase domain, and CD is a conserved domain of unknown function. All other domains are labeled by Pfam family identifier: PF00069 is a protein kinase domain, PF04564 the U-box domain, PF02080 the TrkA domain (unknown function), PF02702 the KdpD domain, PF13493 the DUF4118 domain (unknown function), PF00512 the HisKA domain, PF02518 the HATPase_c domain, PF00999 the sodium/hydrogen exchanger family domain, PF00654 the Voltage CLC domain, PF09413 the DUF2007 domain (unknown function), PF10494 the Stk19 domain (a family of Ser/Thr protein kinases), and PF13520 the AA_permease_2 domain (a family of amino acid permeases).