Characterization of the ush gene of Escherichia coli and its protein products.

The Escherichia coli ush gene has been subcloned and the coding sequence delineated using BAL31 nuclease digestion. Synthesis of proteins encoded by the ush gene have been examined in "maxicells"; two proteins are made, one of which corresponds in Mr (61000) to purified uridine diphosphoglucose hydrolase and the other, less abundant, has an Mr of 43 000. A deletion at the 3' end of the gene introduced by restriction endonuclease digestion, results in the synthesis of a truncated protein of the expected Mr of about 43 000. Precursors of all these proteins are observed in maxicells under conditions known to inhibit processing of secreted proteins. Whereas the precursor of the major ush-encoded protein is retained in the cytoplasm-plus-membrane fraction, unexpectedly the precursor of the truncated protein is secreted. The mature forms of both the normal and truncated proteins are secreted.