CLOSE SIMILARITY AMONG STREPTAVIDIN-LIKE, BIOTIN-BINDING PROTEINS FROM STREPTOMYCES

Two strains of Streptomyces venezuelae were found to produce high-affi nity, biotin-binding proteins, termed streptavidin vl and v2, respecti vely. Both proteins were isolated to purity, and their corresponding g enes were cloned and sequenced. Compared to streptavidin from S. avidi nii, streptavidin v1 had only a single amino acid substitution and str eptavidin v2 showed 9 such differences. The substitutions were remarka bly conservative, none of which affected the amino acid residues known to be important to the biotin-binding properties or to the structure of the tetrameric protein. The results also indicate that the biosynth esis of such biotin-binding proteins is not simply a curious anomaly i n a single species of Streptomyces. It is suggested that the classific ation of S, avidinii as a unique species should be reconsidered. The o ccurrence of these proteins appears to be linked to the production of an unusual synergistic antibiotic complex.