Identification of a celE-binding protein and its potential role in induction of the celE gene in Thermomonospora fusca.

Thermomonospora fusca cellulase E5 is encoded by the celE gene. This gene appears to be regulated at the transcriptional level by both induction and repression, and three putative closely linked promoters have been located by S1 mapping. To study its regulatory mechanism, a gel retardation assay was used to identify a protein in T. fusca cell extracts that interacted specifically with the DNA fragment containing the celE promoters. It was found that the binding activity appeared only when cellulase synthesis was induced, and it therefore resembled an activator protein involved in cellulase induction. DNase I footprinting identified the target sequence for this protein as a 21-base-pair sequence downstream from the putative celE promoters. The level of this protein was measured in two cellulase constitutive mutants, and the results suggest a complex control for celE induction.