Savage (2007) targetted 120 E. coli membrane proteins for in vivo and in vitro expression.
Three targeted proteins were not tested: YbbJ, YeiU, and YeaL.
The remaining 117 proteins are grouped together as the MemProtExpress Topic GeneSet.


Savage et al. (2007) testing expression of 117 N-terminal His-tagged clones in vivo using a pET3-derived vector in BL21(DE3) cells.
In vivo expression, and in vitro expression using S30 extracts, were assessed as negative, weak positive, or strong postive using Western blots.
The primary subdivision into subTopics is MemProtEx-Plus (91 positives) and MemProtEx-Minus (26 negatives).
MemProtEx-Plus is further subdivided into MemProtEx-Both, MemProtEx-Vivo, and MemProtEx-Vitro,
for proteins found to be expressed under both conditions, only in vivo, or only in vitro, respectively.

The expressed proteins are also subdivided into groups based on the level of expression (weak or strong).