REGULATION OF EXPRESSION, GENETIC ORGANIZATION AND SUBSTRATE-SPECIFICITY OF XYLOSE UPTAKE IN BACILLUS-MEGATERIUM

Xylose uptake in Bacillus megaterium depends on expression of a putati ve H+/xylose symporter encoded by xylT, the last gene in the xyl opero n. Insertional inactivation of xylT leads to an apparent uptake defici ency determined with whole cells and severely slower growth on xylose as sole carbon source. Expression of XylT is xylose inducible and subj ect to carbon catabolite repression mediated by CcpA and cre. Northern analysis of the xyl mRNA reveals that a potential stem-loop structure located in the non-translated region between xylA and xylB presumably acts as a transcriptional terminator, as it leads to different amount s of the respective mRNA sections: the 5'-xylA portion is very abundan t, while the 3'-xylBT portion constitutes only a fraction of it. XylT has an apparent Michaelis constant (KM) of approx. 100 mu M and is com petitively inhibited by glucose with an inhibitor constant K-I of 16 m M.