I am using pET28a vector for protein expression. This vector is containing two type of origin of replication i.e pBR322 Ori and f1 Ori. The f1 is the bacteriophage origin of replication which initiates a "rolling circle" replication in phage-infected bacteria. I want to insert OriM (mycobacterial Ori) in place of f1 Ori, so pET28a vector can express in mycobacteria. If I will replace f1 Ori by OriM, will it affect the copy number of pET28a in E. coli (DH5α)?
It shouldn't affect the copy number if you don't want your modified vector late to produce single-stranded plasmid. The f1 origin will only active when a help phage initiates the rolling-circle replication inside the host cells. In the cells without helper phage, a phagemid (plasmid containing a f1 and another Ori) replication is controlled its host specific (E. coli) Ori.
As Huanting suggested, I think this should give no problem for replication in E. coli, and should later work in mycobacterium (although I don't know details of OriM).
Note that your mycobacterium would also need to express a T7 polymerase for the the T7lac-promoter in the modified pET28a to be active in that system. Note, there are already T7-expression systems available: Article Mycobacterium tuberculosis Dihydrofolate Reductase Is Not a ...
no problem, you can to insert OriM (mycobacterial Ori) in place of f1 Ori, without any affect the copy number of the vector in E.coli.
Good luck
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