Fig. 2

Construction of an artificial inducible 39 K promoter. a Analysis of 39 K promoter regulatory element. Purple represents enhancer like components CGTGCGC element, red represents CAAT locus, blue represents transcription inhibitor TGAC box, green represents cis-regulatory original CACT element, and pink represent TATA boxes. Artificial inducible 39 K promoter sequences are underlined. b Relative luciferase assay of the artificial inducible 39 K promoter. BmN-SWU1 cells were co-transfected with the indicated Firefly luciferase and Renilla luciferase expression vector and infected with BmNPV at 10 MOI or uninfected. At 48 h p.i., cells were examined using a luciferase reporter system. Black represents − 773~ − 1 fragment, blue represents + 1~ + 136 fragment and dashed line represents the missing fragment of the 39 K promoter. The regions − 773, − 573, − 273, + 1, + 62 and + 136 represent truncation sites of the corresponding promoter. Red represents the Firefly luciferase reporter gene. The red location represents the CAAT mutation to CGGT of 39 K promoter − 399 site. The blue location represents the CAAT mutation to CGGT of 39 K promoter − 329 site. The Y axis represents different truncated promoters and the X axis represent relative promoter activity of different promoters under infectious and uninfected conditions. The results were calculated as the relative luciferase activity (i.e., Firefly luciferase/Renilla luciferase). The 39 K promoter luciferase activity represents 1 and the promoter activity of the other truncated fragment is a ratio relative to 39 K promoter. BmNPV(+) represents infection with BmNPV, BmNPV(−) represents non-infection with BmNPV. Each data point was determined from the mean of three independent replicates