The discovery of a operon in XL-65-6 coupled with our previous report of a operon (Lai Ingram, 175, 6441-6450, 1993) demonstrates that this thermophilic organism contains all of the genes required for cellobiose uptake by the phosphoenolpyruvate-dependent phosphotransferase system (PTS). Genes encoding the two general PTS proteins, HPr () and enzyme l (), were cloned and sequenced. These form an operon which includes a third small gene () of unknown function (encoded product 18428). Both and were expressed at high levels from a single plasmid in and complemented corresponding host mutations. Although the translated sequences for these genes were similar to homologues from Gram-positive mesophiles (64-77% identity), the gene products were unusual in having a higher predicted pi and fewer negatively charged amino acid residues. Enzyme I also contained more alanine and leucine than mesophilic counterparts. Interestingly, inhibited the growth of mutants at 37°C. No such inhibition was observed during incubation at a lower temperature (30°C) or in DH5, which is wild-type for . The predicted translation product from contained a high proportion of basic amino acids (27%) and had a high predicted pl (pH 117), properties similar to bacterial histone-like proteins, but did not exhibit homology to any sequences in the current database. Regions upstream and downstream from the operon contain genes with homology to and (wall-associated protein), respectively.


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