X0306 4 2019-12-12 0 0001426800 ASSEMBLY BIOSCIENCES, INC. ASMB 0001663018 Colonno Richard James C/O ASSEMBLY BIOSCIENCES, INC. 11711 N. MERIDIAN ST., SUITE 310 CARMEL IN 46032 0 1 0 0 EVP & CSO, Virology Ops Common Stock 2019-12-12 4 M 0 33061 7.03 A 160882 D Common Stock 2019-12-12 4 S 0 33061 25.0016 D 127821 D Stock Option (right to buy) 7.03 2019-12-12 4 M 0 33061 0.00 D 2026-01-11 Common Stock 33061 166939 D The option exercise and sale reported on this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person. Includes 532, 1,000 and 39 shares acquired under the Assembly Biosciences, Inc. 2018 Employee Stock Purchase Plan on November 14, 2018, May 14, 2019 and November 14, 2019, respectively. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $25.00 to $25.035, inclusive. The reporting person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within. This option represents a right to purchase 200,000 shares. As of January 5, 2019, 150,000 stock options have vested. The remaining options vest on January 5, 2020. /s/ John O. Gunderson, as Attorney-in-Fact 2019-12-16