“…Of the three GBL receptors in S. avermitilis, AvaR1 acts as an avenolide receptor to control avenolide and avermectin production by directly repressing the transcription of aco, aveR, its own gene and the other two GBL receptor homologous genes (avaR2 and avaR3) (Figure 3; Zhu et al, 2017). ScbR2, JadR2, AvaR2 and SabR2 were identified as pseudo GBL receptors (Xu et al, 2010;Zhu et al, 2016;Wang et al, 2018), and the roles of these pseudo GBL receptors in the regulation of antibiotic biosynthesis will be discussed in a subsequent section. AvaR3 contains an extra 75amino acid stretch that is not present in typical GBL receptors, and promotes avermectin production through a yet-unknown regulatory mechanism (Miyamoto et al, 2011).…”