THE ESCHERICHIA-COLI GAPA GENE IS TRANSCRIBED BY THE VEGETATIVE RNA-POLYMERASE HOLOENZYME E-SIGMA(70) AND BY THE HEAT-SHOCK RNA-POLYMERASE E-SIGMA(32)

Escherichia coli D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is produced by the gapA gene and is structurally related to eukaryotic G APDHs. These facts led to the proposal that the gapA gene originated b y a horizontal transfer of genetic information. The yields and start s ites of gapA mRNAs produced in various fermentation conditions and gen etic contexts were analyzed by primer extension. The transcriptional r egulatory region of the gapA gene was found to contain four promoter s equences, three recognized by the vegetative RNA polymerase E sigma(70 ) and one recognized by the heat shock RNA polymerase E sigma(32). Tra nscription of gapA by E sigma(32) is activated in the logarithmic phas e under conditions of starvation and of heat shock. Using a GAPDH(-) s train, we found that GAPDH production has a positive effect on cell gr owth at 43 degrees C. Thus, E. coli GAPDH displays some features of he at shock proteins. One of the gapA promoter sequences transcribed by E sigma(70) is subject to catabolic repression. Another one has growth phase-dependent efficiency. This complex area of differentially regula ted promoters allows the production of large amounts of gapA transcrip ts in a wide variety of environmental conditions. On the basis of thes e data, the present view of E sigma(32) RNA polymerase function has to be enlarged, and the various hypotheses on E. coli gapA gene origin h ave to be reexamined.