Expression patterns of cel5A-cel5B, two endoglucanase encoding genes of Thermobifida fusca

Expression patterns of cel5A and cel5B, two endoglucanase encoding genes of Thermobifida fusca were compared by quantitative real-time PCR. With Avicel as carbon source the transcript level of cel5A continuously increased until the 10th hour of incubation and then a sharp decrease was observed, whereas cel5B presented a slow constitutive expression on this substrate. When the microcrystalline cellulose powder MN300 was used as the inducing carbon source, the expression patterns of the two genes were similar. A low initial level of expression was followed by a rapid increase at the 5th hour of incubation; a transient repression was then observed at the 10th hour but after this sampling time, the expression levels started to increase again. The relative expression levels of cel5A were always higher than those of cel5B. Differences in transcription patterns of these two genes can be explained with the imperfect structure of the CelR binding regulatory region of cel5B.