Modified pENTR vectors. Epitope tags were introduced in the pENT-STOP vector between the att L1 and att L2 recombination sites to generate modified pENTR vectors both for N-terminal (A) and C-terminal (B) tagging (pE1n-pE6n and pE1c-pE6c respectively). The amino-acid composition of the short linkers added between the tag and the protein and their reading frame with respect to the target sequence is shown for all the constructs. The Bam H I and Not I sites are underlined. A thrombin cleavage site is present in pE4n for protein purification purposes.