1

Expression plasmids used We used a plasmid expression system with well established components, closely analogous to the widely employed pQE30 backbone (a commercial vector from Qiagen). As shown in Figure S1, it consists of the strong inducible T5 promoter under control of two lac-operator sequences in series [1], the ORF of the protein of interest, followed by two terminators in series (a T7 transcription terminator and a strong rrnB t1 transcription terminator [2]), a ColE1 origin of replication (as present in pBR322, but without the rop gene [3]), the -lactamase gene under its own promoter to confer resistance to ampicillin with the strong transcription terminator t0 of phage , and, facultatively, the lacI gene coding for the lac repressor, which is under control of the lacI q promoter and terminated by the strong tHP terminator [4], for tight regulation of the operon. The expression vectors used (summarized in Table S1) are called pMPAG77 (without lacI gene cassette), and pMPAG6 (carrying a lacI gene cassette under the lac