The term minicell was introduced by Adler et al. (1 ) for the small spherical cells produced by abnormal cell division at polar ends of certainEscherichia colicells. The phenomenon itself however, had already been described as early as 1930 (2 ) for a strain ofVibrio cholera. These minicells do not contain any chromosomal DNA, but they do inherit in most cases the plasmid DNA present in the parental strain. Since plasmid-containing minicells are able to synthesize DNA, RNA, protein, and other cell components, they are specifically suited for the in vivo analysis of the gene products encoded for by their plasmid contents, in the absence of gene products encoded for by the host genome. In this chapter the isolation of minicells will be described, whereas the identification of gene products in minicells will be described in Chapter 48 . Other methods currently used to analyze the gene products of a particular stretch of DNA are the maxicell system (Chapter 47 ) and the various DNA-dependent in vitro protein synthesis systems (Chapter 19 ).
