The Construction of pBR322Δrop and Its Interaction with pUC19 with Respect to Plasmid Copy Number and the Exclusion Effect

When pBR322 is co-transfected with pUC19, pBR322 is excluded from the host bacterial cell in what is known as the exclusion effect. The pBR322 plasmid encodes the rop gene that regulates copy number, which pUC19 lacks and thus has a high copy number. The rop gene was removed from pBR322, to create pBR322 ∆ rop, to investigate whether Rop is responsible for a decreased plasmid copy number and is thus the cause of the exclusion effect. Cotransfections of pUC19 with either pBR322 or pBR322 ∆ rop were performed in Escherichia coli DH5 α to determine if pBR322 ∆ rop would be able to evade the exclusion effect. Through selection with antibiotics and blue and white colony screening, it was found that when pUC19 was co-transfected with pBR322 ∆ rop, the pBR322 derivative had evaded the exclusion effect as there was a greater frequency of white colonies, which contained only pBR322 ∆ rop. However, there were seven times more white colonies than blue colonies, suggesting the absence of pUC19 in most of the colonies. This implies that there is a possibility that pUC19 is excluded out of the E. coli when co-transfected with pBR322 ∆ rop. Nonetheless, since such a small population was analyzed in this experiment, because of time constraints, further experiments should be performed to confirm the possible exclusion effect of pUC19 by pBR322 ∆ rop.