pUR 250 allows rapid chemical sequencing of both DNA strands of its inserts.

A multipurpose plasmid, pUR 250, has been constructed. It contains seven unique cloning sites (Hind III, Xba I, Sal I, Acc I, Hinc II, BamH I and EcoR I) in a small region of its lac Z gene part. Insertion of foreign DNA into the plasmid can be easily detected. Plasmid DNA isolated from a clone by a rapid method can be used to determine the DNA sequence of the insert from both ends directly without isolation of labeled fragment.