A new Comamonas testosteroni steroid-inducible gene: cloning and sequence analysis.

Comamonas testosteroni can grow on a variety of steroid compounds as the sole carbon and energy source. In a previous study, we cloned and sequenced the testosterone-inducible betahsd gene from C. testosteroni (Genti-Raimondi, S., Tolmasky, M., Patrito, L., Flury, A. and Actis, L., Molecular cloning and expression of the beta-hydroxysteroid dehydrogenase gene from Pseudomonas testosteroni. Gene, 1991, 105, 43-49.). Herein we report the cloning and characterization of another steroid-inducible gene (stdC), located 2400 bp upstream of betahsd. Nucleotide sequencing of a region encompassing the stdC gene revealed an open reading frame 546 bp long including the stop codon TGA with significant similarity to the orf4, orf1 and orf4 of unknown function described in the polyhydroxyalkanoic acid (PHA) cluster of Chromatium vinosum, Rhizobium meliloti and Thiocystis violacea, respectively. The aminoacid sequence deduced from the nucleotide sequence predicts a putative protein of 181 amino acids with a molecular weight of 20715 Da. Northern blot experiments indicate that the stdC gene was transcribed as a monocistronic mRNA with an apparent molecular size of 670 nt. The stdC transcript was abundant in C. testosteroni cells grown with different steroid carbon sources harvested in the exponential phase and was found to be under catabolite repression.