Figure 17.3: Vector map of pBR 322

pUC19: pBR322 was constructed in 1977 and since then large number of plasmids have been derived from this plasmid to achieve specific requirement of an application. It was mainly done by adopting different screening strategies than pBR322 and addition of other structural features. In the similar advancement, a multiple cloning sites were added to facilitate easy cloning without disrupting antibiotic resistance gene. pUC19 is the intial example of bacterial plasmid of small size (2.8Kb) containing multiple cloning site (Figure 17.4). The usual place to keep the MCS is always between initiation codon (AUG) and the codon 7. An MCS allow design of many cloning strategies as the large number of enzyme available for cloning. In addition, two enzymes from MCS can be used to insert the foreign DNA without disturbing plasmid sequences. pUC 19 vector also has a small stretch of DNA which encodes for rapid detection of an insert by blue-white screening. The details of different screening methods are discussed in future lecture.