Shell component of a type 2A encapsulin nanocompartment. Expression in E.coli generates nanocompartments with an average diameter of 25 nm. They can be disassembled by treatment with 6M guanidine hydrochloride and reassembled with cargo. The nanocompartment is probably involved in sulfur metabolism (PubMed:33821786). Probably allows passage of cysteine into its interior; during growth in light the physiological pH is 8-8.4, about 30-54% of free cysteine (charge -1) would be able to pass through the shell (Probable). The 24.5 nm encapsulin nanocompartment is formed by 60 subunits; monomers form pentamers which assemble to form shells. There are 12 positively charged pores where the pentamers meet with a minimal pore diameter of 3.7 Angstroms as well 3-fold axis channels and dimer channels. Unlike type 1 subfamily encapsulins, the nanocompartment has a raised protuberance around the 5-fold pores. Transcriptionally induced in the absence of sulfur, requires CysR for transcription. Part of the srpG-srpH-srpI operon (PubMed:7603442). Present in when grown in sulfur-containing media, induced 7-fold after 48 hours of sulfur starvation (at protein level) (PubMed:33821786). Has 4 domains; an N-terminal arm not found in the type 1 subfamily, a discontinuous peripheral domain (P), an elongated loop (E) and the discontinuous axial domain (A). No growth phenotype of a single sprI or double srpI-cyd deletion mutant in the presence or absence of sulfur. Belongs to the encapsulin family. Family 2A subfamily.