Encapsulin assembly and classification. (a) Representative cryogenic electron micrographs of differently sized encapsulin shells: T1, Thermotoga maritima; T1 + cargo, Acinetobacter sp. 1289694; T3, Kuenenia stuttgartiensis, and T4, Quasibacillus thermotolerans. (b) Schematic outlining concurrent Family 1 encapsulin cargo loading and shell self-assembly. (c) Four-family classification scheme for encapsulins based on sequence similarity and genome neighborhood analysis. Question marks indicate experimentally unconfirmed cargo proteins or enzymatic components. Abbreviations: cNMP, cyclic nucleotide; Enc, encapsulin.