The Use of Minicells and Maxicells to Detect the Expression of Cloned Genes

Abstract

An analysis of cloned DNA fragments involves the characterisation of the products of gene expression and the regulation of their synthesis. When it is known that a DNA fragment codes for a particular protein or RNA species, suitable tests can be devised to determine if the cloned DNA is expressed in a particular host and the subcellular localisation of the products can be investigated. Thus, proteins can be detected by sensitive immunoassays, RNA by hybridisation to suitable probes and enzymes by appropriate enzyme assays. But how does one detect expression of genes on cloned DNA fragments when the function of the gene products is not known or if no suitable detection assays are available? The answer is to look for the synthesis of novel polypeptides or RNA species in cells carrying the cloned DNA fragments. However in wild-type cells the detection of new proteins and RNA species is almost impossible because of the concurrent expression of the host genome. Three approaches have been devised to circumvent this problem and to detect expression of cloned DNA (plasmid DNA) borne gene products: DNA-driven in vitro protein and RNA synthesis; minicells and maxicells.