Fig. 1

Schematic diagram of the composition and function of the spn gene cluster. The 19 genes of spn were divided into 9 co-transcription units (U1, U2, U3, U4, U5, U6, U7, U8, and U9) and are shown by black arrows. According to their functions, the 19 genes can be divided into four groups, each represented by a different color