Cell-free coupled transcription-translation system for investigation of linear DNA segments.

Heretofore the DNA-directed coupled transcription-translation system, most useful in gene expression analysis, has been limited to the use of circular or long linear DNAs. Linear DNAs are degraded in this system by an exonucleolytic activity that can be eliminated by making the synthetic extracts from a suitable recB mutant of Escherichia coli. Using these extracts, we have examined the gene expression of a variety of linear DNAs. In particular, the complex pattern of expression of ribosomal protein genes and RNA polymerase genes in the rpoBC-rplLJ region has been analyzed by comparing the protein products obtained when using lambda rifd18 DNA with the product obtained when using the same DNA segmented with various restriction enzymes. The results obtained confirm the conclusions of others obtained by much more elaborate in vivo techniques. It seems highly likely that this cell-free system will have extensive applications in the area of analysis of gene expression.