This family consists of several bacterial CreD or Cet inner membrane proteins. Dominant mutations of the cet gene of Escherichia coli result in tolerance to colicin E2 and increased amounts of an inner membrane protein with an Mr of 42,000. The cet gene is shown to be in the same operon as the phoM gene, which is required in a phoR background for expression of the structural gene for alkaline phosphatase, phoA. Although the Cet protein is not required for phoA expression, it has been suggested that the Cet protein has an enhancing effect on the transcription of phoA [1].

1: Identification and sequencing of the Escherichia coli cet gene which codes for an inner membrane protein, mutation of which causes tolerance to colicin E2. Drury LS, Buxton RS; Mol Microbiol 1988;2:109-119. PMID:2835585