Variants of M13 gp9 proteins. Schematic overview of the gp9 variants used in this work. Into the wild-type a MunI restriction site was introduced between codon 2 and 3 resulting in two additional residues in gp9MunI (A). Into this MunI site short sequences were introduced encoding for the T7 tag in gp9-T7 (B) and for the HA tag in gp9-HA (C). In addition, a double tag was introduced into gp9 generating gp9-DT7 (D) and gp9-DHA (E), respectively. The protein sequence of each mutant is given in the single letter code.