[DIYbio] Re: pBLU and pBluescript

The LacZ gene can be broken in two expression units - LacZ-alpha and LacZ-omega. The pBluescript (and pUC series) plasmids, as Koeng pointed out, has the much smaller LacZ-alpha gene. LacZ-alpha by itself will not give you beta-gal activity. If you use this then you will need a bacterial host (e.g. DH5-alpha) that contains the omega gene fragment - lacZΔM15. The combination of the alpha and omega gene products produces functional beta-gal activity in what is call alpha-complementation. So it depends on what you want to do in your experiment as to which plasmid to use. Full length lacZ will allow you to express beta-gal in almost any cell type but if you want to do blue/white selection then you will need alpha-complementation with the appropriate plasmid and host.