PROTEIN SECRETION IN ESCHERICHIA-COLI K-12 - DEAD OR ALIVE

Escherichia coli K-12 possesses a large number of chromosomal genes th at, in other Gram-negative bacteria, are involved either in exoprotein secretion or in the formation of type IV pili. Some of these E. coli genes have been shown to encode proteins when expressed from heterolog ous promoters. Furthermore, at least two of these proteins are functio nal in heterologous complementation tests, but none of the genes exami ned so far is expressed when E. coli is grown under standard laborator y conditions. We propose that transcription of these genes is turned o ff during growth in laboratory medium, that their expression is contro lled by environmental sensor proteins and that they could play an impo rtant role in pathogenicity or in the utilization of large polymers.