The mNeongreen gene was cloned into pOPINE-His vector for mammalian protein expression and pOPINO-His vector for bacterial expression Cell culture EXPI293 cells (A14527, Thermo Fisher) were used to express mNeongreen to generate mNeongreen mammalian lysate. The EXPI293 cells were grown in EXPI293 medium (A1435101, Thermo Fisher) at 37 °C, 125 rpm, 5% CO2 atmosphere with at least 75% humidity in plastic flasks with ventilated caps (Corning Erlenmeyer sterile polycarbonate with 0.2um ventilated caps). For transfection, 20 mL of EXPI293 cells with 1 million cells/mL concentration in plastic flasks with ventilated caps were taken on the first day. The following day, 20 ug of plasmid DNA and 107ul of PEI MAX (40 kDa) was diluted in 2 mL OptiMEM media, and the mixture allowed to incubate for 10 minutes at room temperature (22 °C), transfected by slowly pipetting the PEI/DNA mixture into EXPI293 cells. The cells were collected after 48 hrs of post-transfection.