Restriction endonuclease-generated DNA fragments of lambda polC-9 (Friesen et al. 1976) have been cloned on plasmid vehicles. Expression of genes carried by these plasmids was determined either by genetic complementation of the appropriate mutants, or in ultraviolet-irradiated cells. On the basis of these experiments we have inferred the following gene order in the four minute region of the Escherichia coli chromosome: tonA-dapD4-dapD2-rpsB-tsf-22 kilodalton protein - fir 27,000-firA-dnaE. We suggest that rpsB and tsf are in one transcriptional unit, with rpsB being promoter-proximal. We also suggest the possible position of the promoter for dnaE.