pComb3X is the newest of the pComb vectors. Improvements over pComb3 include increased stability and introduction of SfiI cassette for cloning of full Fab, scFv, peptide and other protein for phage display. 6xHis and HA tags allow for purification and detection. An amber stop codon was introduced to turn-off expression of the pIII fusion protein by switching to a non-supressor strain of E. coli allowing production of soluble protein without subcloning. Alternatively, the gene for phage protein pIII can be removed by SpeI/NheI digest. pComb3XSS is the vector we normally ship. The “SS” refers to the double stuffer, a 1200bp stuffer in the Fab light chain cloning region bounded by SacI and XbaI restriction sites and a 300bp stuffer in Fab heavy chain cloning region bound by XhoI and SpeI restriction sites. Also, the 1600bp double stuffer (both stuffer plus the leader sequence between the Fab light chain and heavy chain cloning regions) can be removed by SfiI digest so that non-Fab genes of interest can also by cloned.