The ptsH, ptsI, and crr genes of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system: a complex operon with several modes of transcription

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Abstract
The ptsH, ptsI, and crr genes, coding for three of the proteins of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) (HPr, enzyme I, and enzyme IIIGlc, respectively) have been studied by determination of their nucleotide sequence and analysis of their expression. The three genes constitute an operon, but analysis of the ptsH, ptsI, and crr transcripts by Northern (RNA) blotting revealed the existence of three major mRNA species. One encompassed the three cistrons, a second one the ptsH gene and part of the ptsI gene, and the third one only the distal gene crr. The short crr transcripts were initiated inside the ptsI open reading frame at points which were identified by S1 mapping. Expression of the genes was studied in vivo by using operon and protein fusions between the lacZ gene and the ptsH, ptsI, or crr gene on IncW low-copy-number plasmids. The present study showed that (i) the ptsH, ptsI, and crr genes exhibited high basal expression, (ii) transcription of the ptsH and ptsI genes was stimulated threefold by the cyclic AMP-cyclic AMP receptor protein complex and also by growth on glucose, but only in the presence of an active enzyme IIGlc, (iii) crr-specific expression was not sensitive to the complex or to growth on glucose, and (iv) under the growth conditions tested, the major part of crr transcription was initiated from internal promoters.

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