The λ bacteriophage's PV protein makes up the tubular portion of its tail. The tubular structure comes with 32 discoidal substructures, each of which comprises six PV subunits. PV has two folding regions. Exogenous sequences can be inserted into the folding structural domain (the non-functional region) at the C-terminus. The assembly of λ bacteriophages occurs inside cells, which enables the presentation of hard-to-secrete peptides or proteins. The phage display system showed an average copy number of foreign proteins of one molecule per phage, suggesting that foreign proteins or peptides might interfere with the tail-assembly of λ bacteriophages.