Derivatives of pUC18 that have BglII sites flanking a modified multiple cloning site and that retain the ability to identify recombinant clones by visual screening of Escherichia coli colonies.

We report the construction of a series of derivatives of pUC18 in which a modified multiple cloning site is flanked by one or two BglII sites. The reading frame of the lacZ alpha fragment was retained in each construct, permitting the recognition of transformants containing plasmids with inserts by visual screening for loss of blue coloration.