The upward vertical arrow from NagB with an X in the middle and a similar downward arrow from AgaS indicate that AgaS and NagB do not substitute for

each other. Although the functions of the genes in the aga/gam cluster were initially surmised from in silico studies, there are some experimental data now that support the predicted functions of ten of the thirteen genes. Genetic and transport studies in E. coli C and in E. coli K-12 support the prediction of the PTS genes in the aga/gam cluster [6, 9]. The induction of tagatose 1, 6-BP aldolase activity by Aga and Gam along with other complementation studies demonstrates that kbaY codes for the aldolase Sepantronium mw [6, 10] and kbaZ codes for the subunit that is needed for full activity and stability in vitro[10]. It has been shown that the agaR encoded repressor Ilomastat clinical trial binds to promoters BIIB057 solubility dmso upstream of agaR, kbaZ, and agaS (Figure 1) [11]. That agaA codes for Aga-6-P deacetylase was indirectly implied because

Aga utilization was unaffected in a nagA mutant [6]. The assigned role of the agaI gene as Gam-6-P deaminase/isomerase had not been tested and what, if any, role the agaS gene plays in the Aga/Gam pathway was not known although it was predicted to code for a ketose-aldose isomerase [1, 6, 11]. The interest in the Aga/Gam pathway stems from our earlier finding that isolates of the foodborne pathogen, E. coli O157:H7, from Farnesyltransferase a spinach outbreak could not utilize Aga because of a point mutation in EIIAAga/Gam (Gly91Ser) [12]. We also pointed out that E. coli O157:H7, strains EDL933 and Sakai, harbor two additional point mutations in agaC and agaI. Both mutations change a CAG codon coding for glutamine to TAG, an amber stop codon: one in the eighth codon of the agaC gene that codes for EIICGam; and the other in the 72nd codon of the agaI gene that had been proposed to code for Gam-6-P deaminase/isomerase. Although these two mutations reside in both EDL933 and Sakai strains, the annotations are different

in these two strains. In EDL933, agaC is annotated as a 5’ truncated gene and agaI is annotated as a split gene (Figure 1) whereas, in the Sakai strain they are not annotated at all [12]. In E. coli O157:H7, the amber mutation in agaC affects EIICGam which explains the Gam- phenotype but the mutation in agaI does not affect utilization of Aga as the sole source for carbon and nitrogen [12]. The obvious question that arises is how does this happen without an active Gam-6-P deaminase/isomerase. E. coli K-12 is Aga- Gam- but isolation of suppressor mutants of E. coli K-12 with mutations in the GlcNAc regulon that were Aga+ Gam- has been reported [6]. These mutants transported Aga by the GlcNAc PTS and since nagA was required for Aga utilization it was inferred that NagA deacetylated Aga-6-P. Based on these findings we had hypothesized, by analogy, that nagB might similarly substitute for agaI in E.

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