Fig. 4. The M1249L D2-D4 domains, through structural analysis, are identified as a temporary transcription factor analogous to TFIIB.

a The surface structure of vRNAP-M1249L, highlighting the functional domains of M1249L, shows similarities to the classical transcription factor TFIIB (cyan dashed box). b Comparison of the location of M1249L TFIIB-like domains to human, S.cerevisiae TFIIB and VACV Rap94 B-homology region. The whole model is shown as a transparent blue surface with TFIIB or TFIIB-like domain shown in cartoon. c The four structures of TFIIB shown in the cartoon. The Zn²⁺ ions in Zinc-finger motifs are shown as blue spheres. The similar domains are indicated by dashed circles of the same color. d Four maps illustrate the M1249L TFIIB-like domain dynamic alterations.