With regard to transcriptional regulation of thefru operon , the results summarized here and previously , as well as unpublished results -LRB- Cao and Saier -RRB- suggest that the fru regulon in S. typhimurium is complex ; that it may consist of at least three or four operons , one encoding the IIIFm-FPr protein , fructose-i-phosphate kinase , and IIFru , a second encoding a fructose-inducible enzyme I-like protein , a third encoding the fructose repressor , FruR , and possibly a fourth encoding a cryptic 11Fru -LRB- Cao and Saier , unpublished results -RRB- ; that it is unique in its response to the loss of the cyclic AMP-CRP complex as a result of mutations in the cya , crp , or pts gene ; that it may be regulated at the transcriptional level by two or more distinct mechanisms -LRB- possibly involving two distinct inducers , fructose-i-phos-phate and fructose -RRB- which together account for induction by fructose , or that low-level expression of cryptic fru genes accounts for the anomalous fru operon induction behavior ; and that the proteins of the fructose-specific PTS may play a direct or indirect role in transcriptional regulation .