Fig. 3. The unique β-strand latch of hPIV3 L RdRp for transient positioning of CTD.

a The β-strand latch extended from hPIV3 L RdRp forms interactions with L CTD. The domains of hPIV3 L are colored as depicted in Fig. 1a. The β-strand latch (Phe641–Lys644) of hPIV3 L RdRp is labeled. The disordered region followed by the β-strand latch is shown as a dotted line. Magnified view of the interactions between β-strand latch and CTD of hPIV3 are shown in the left panel and the polar interactions are indicated by dashed lines. b Western blot to confirm the expression of FLAG-tagged variant L proteins with mutations on the β-strand latch. Representative gel and quantification of the protein levels relative to that of the FLAG-tagged wild-type (WT) L are shown in the upper and lower panels, respectively. c Luciferase-based minigenome assay to evaluate the polymerase activity of the β-strand latch mutants. The mutants with substitutions on the RdRp catalytic residue Asp773 or HR motif (His1290 and Arg1291) of PRNTase domain, which would be expected to inhibit polymerase activity are used as negative controls. Luciferase levels are normalized to an internal control and then to FLAG-tagged WT L, which is set to 100%. Relative luciferase units, RLU. The bars in b and c show the mean and standard deviation for three independent experiments (the data points for each experiment are shown). d The C-terminal β-strand tail of VSV L CTD that may have similar function. The C-terminal β-strand tail (β-strand Ser2106–Asp2109 with the upstream loop) of VSV L CTD is labeled. Source data are provided as a Source Data file.