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Diagram of the viral variants generated by site-directed mutagenesis. Briefly, the Leu-214 (214L) polymorphism was introduced in the pNL4-3 background, which contained the Phe-214 (214F) variant. Trp-210 (210W), Tyr-215 (215Y), or Phe-215 (215F) was then combined with each of these Phe-214 and Leu-214 backgrounds.
