A minor shell protein of the bacterial microcompartment (BMC) dedicated to 1,2-propanediol (1,2-PD) degradation. The isolated BMC shell component protein ratio for J:A:B':B:K:T:U is approximately 15:10:7:6:1:1:2 (PubMed:12923081). Not required for structural integrity of BMCs nor to mitigate propionaldehyde toxicity, it might be involved in spatial organization of BMCs (PubMed:21239588). The 1,2-PD-specific bacterial microcompartment (BMC) concentrates low levels of 1,2-PD catabolic enzymes, concentrates volatile reaction intermediates thus enhancing pathway flux and keeps the level of toxic, mutagenic propionaldehyde low. The C-terminal 70 residues (positions 90-160) when overexpressed in E.coli bind Fe (PubMed:20870711). Might bind an [Fe-S] cluster in vivo (Probable). Polyol metabolism; 1,2-propanediol degradation. Interacts with shell proteins PduA and PduP and assembly protein PduM. BMC production is induced by growth on 1,2-PD vitamin B12 medium. Releases increased amounts of acetaldehyde when grown on propanediol (PubMed:16585748). Half the cells seem to form BMC aggregates with visible shells, the other half have no BMCs. Grows normally on 1,2-PD and vitamin B12 (PubMed:21239588). A double pduJ-pduK strain grows in an interrupted manner on 1,2-PD and vitamin B12; grows for a while then stops, then restarts as toxic propionaldehyde accumulates and then decreases (PubMed:18296526). Artificial BMCs can be made in E.coli by expressing pduA-pduB/B'-pduT-pduU-pduN-pduJ-pduK (in this order). Enzymes can be targeted to the BMC, and appear to be encapsulated within it. Bacterial microcompartments (BMC) 100-200 nm in cross section are formed during aerobic growth on minimal 1,2-PD-B12 or anaerobic growth on 1,2-PD-tetrathionate medium, but not during aerobic growth on glucose, anerobic growth on glucose or pyruvate-tetrathionate (PubMed:10498708). BMCs can constitute up to 10% of total cell protein (PubMed:12923081). Belongs to the bacterial microcompartments protein family.