Every bloody protocol suggests adding in DTT when doing in vitro RNA transcription. Why? The rationale seems to be that the cytoplasm traditionally has a reducing environment but as the only protein we care about is the T7 polymerase, why is this necessary.
A quick search on T7 cysteines gave some clues:
There's a more recent paper (Aguirre et al, Inorganic Chemistry 48:4425 (2009)) that mentions the "the enzyme critical sulfhydryl cysteine groups", but unfortunately I only have access to the abstract.
Update: It seems to be an old finding, rather than a rationale concerning the cytoplasmic redox state. According to Chamberlin and Ring, JBC 248:2235 (1973),
(no surprises there ;)
However, if you see the table I, the remaining activity after removing bme is still 74%
There seems to be 7 exposed cysteines (Mukherjee et al, Cell 110:81 (2002)), but I could not find any paper discussing their roles.
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