Cloning and expression of uncI, the first gene of the unc operon of Escherichia coli.
The unc operon of Escherichia coli consists of eight genes coding for the eight subunits of the proton-translocating ATPase. In vitro transcription-translation of DNA cloned from the beginning of the operon onto plasmids reveals that the reading frame uncI, which precedes the other genes of the operon, codes for a protein with a molecular weight of 14,500, called i. In minicells, the i protein is synthesized in amounts comparable to the amounts of the ATPase subunits, suggesting that it may be part of the ATPase complex. The presence of the unc promoter and uncI on a plasmid containing the other eight genes of the unc operon has little effect on the differential expression of the unc genes or the partitioning of the newly synthesized subunits into soluble or sedimentable fractions in the in vitro system. The i protein partitions into the sedimentable fraction.