Complex sentence: The standard plasmids used for determination of transformation efficiency in "Escherichia coli" are pBR322 or the smaller pUC series of vectors, different vectors however may be used to determine their transformation efficiency.
Split into simpler sentences: The standard plasmids used for determination of transformation efficiency in "Escherichia coli" are pBR322 or other similarly-sized vectors, such as the pUC series of vectors. Different vectors however may be used to determine their transformation efficiency.