<jats:title>ABSTRACT</jats:title> <jats:p> The SAV3339 (SdrA) protein of <jats:named-content content-type="genus-species">Streptomyces avermitilis</jats:named-content> , a member of the DeoR family of regulators, was assessed to determine its <jats:italic>in vivo</jats:italic> function by gene knockdown through the use of <jats:italic>cis</jats:italic> -encoded noncoding RNA and knockout of the <jats:italic>sdrA</jats:italic> gene. These analyses revealed that SdrA represents another class of <jats:named-content content-type="genus-species">Streptomyces</jats:named-content> regulator that controls morphological development and antibiotic production.