we keep pEX2 plasmids in XL1-Blue.  You might find this table helpful in comparing how pop2136 compares https://www.addgene.org/mol_bio_reference/strain_information/

Dear Joannie Kamens,

thank you for your reply, I keep the plasmid in XL1-Blue too, but I have problems during the induction - some of clones are without any traces of target protein after induction. I can explain it by the problems with plasmid stability during the cultivation of bacteria...

Do you have any experience in induction of protein?

thanks