Rapid control of protein abundance is crucial in both basic and applied research. Small molecule-controlled protein expression is promising tools for such rapid control. However, concerns arise regarding the residual chemicals in cells treated with these molecules, especially when recombinant proteins are intended for medical purposes. The small molecule-assisted shut-off (SMASh) utilizes inhibitors against hepatitis C virus (HCV) non-structural protein 3 protease, enabling use of the Pharmaceuticals and Medical Devices Agency (PMDA)-approved, less concerning chemicals for the target protein control. In this study, we developed SMASh-tagged enhanced green fluorescent protein (EGFP) reporters to evaluate the efficacy of SMASh and confirmed its functionality in the Bombyx mori-derived ovary cell line, BmN. Upon comparing degron efficiencies, we discovered that the HCV-derived degron in the SMASh tag was more effective at degrading the fused EGFP than the commonly used PEST sequence of mouse ornithine decarboxylase. The activity of the SMASh tag was quantitatively tunable within the range of 10⁻³ to 1 mM of Asunaprevir in BmN cells. Higher concentrations, such as 5 µM, were toxic to the cells. We also revealed the irreversibility of SMASh-mediated gene suppression in BmN cells. Our findings pave the way for achieving rapid and robust suppression of target protein expression with PMDA-approved drugs in silkworm biology.

 The paper entitled “19G1-30 kDa proteins in the membrane of the pupal fat body of Bombyx mori in- teract with a hemolymph chymotrypsin inhibitor” by Yoshinori Ueno, Taro Okada, Ningjia He, Minoru Ujita, Yutaka Banno and Zenta Kajiura that appeared in Journal of Insect Biotechnology and Sericology, Vol. 91, No. 3, pages 33 to 39, contained an error in authors on page 33. It should appear as follows:

 Yoshinori Ueno1#, Taro Okada2, Ningjia He3, Minoru Ujita4, Yutaka Banno1, Koji Shirai5, Hiroshi Fujii1 and Zenta Kajiura5＊

 1Institute of Genetic Resources, Faculty of Agriculture, Kyushu University, Nishi-ku Motooka 744, Fukuoka 819-0395, Japan

 2PhoenixBio Co., Ltd, TechnoPlaza #405, 3-13-26, Kagamiyama Higashihiroshima 739-0046, Japan

 3State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400715, China

 4Laboratory of Biological Chemistry, Department of Applied Biological Chemistry, Faculty of Agriculture, Meijo University, Nagoya 468-8502, Japan

 5Faculty of Textile Science and Technology, Shinshu University, Tokida 3-15-1, Ueda 386-8567, Japan