THE ALGT (ALGU) GENE OF PSEUDOMONAS-AERUGINOSA, A KEY REGULATOR INVOLVED IN ALGINATE BIOSYNTHESIS, ENCODES AN ALTERNATIVE SIGMA-FACTOR (SIGMA(E))

Chronic infection by alginate-producing (mucoid) Pseudomonas aenuginos a is the leading cause of mortality among cystic fibrosis (CF) patient s. During the course of sustained infection, the production of an algi nate capsule protects the bacteria and allows them to persist in the C F lung. One of the key regulators of alginate synthesis is the algT (a lgU) gene encoding a putative alternative sigma factor (sigma(E)), Alg T was hyperproduced and purified from Escherichia coil. The N-terminal sequence of the purified protein matched perfectly with that predicte d from the DNA sequence. The purified protein, in the presence of E. c oil RNA polymerase core enzyme, was able to initiate transcription of an algT promoter. Deletion of the -35 region of this promoter abolishe d this activity in vitro as well as in vivo. These data indicate that the algT gene encodes a sigma factor that is autoregulatory.