Fig. 4. Path of the PPT loop in hC*.

(A) Schematic of RNAs in the RNP core of the PM5 hC* complexes. Yellow balls, positions of the catalytic Mg²⁺ ions M1 and M2, as well as structural Mg²⁺ ions M3-M5. (B) Overview of the path of the PPT loop and 5′ end of the 3′ exon mimic (3′ exon*). (C and D) Tight fit of the 5′ region (C) and 3′ region (D) of the PPT loop, with space filling models of proteins forming the PPT loop pocket. (E) Electrostatic surface potential of proteins forming the PPT loop pocket, where blue indicates a positive charge and red indicates a negative charge. (F) Extended positive surface of CACTIN. Dashed line, the potential path for nucleotides of introns with a longer distance between the BS-A and 3′ss.