SHFL and HIV infectious disease: As a control for inhibition of −1PRF, we transiently overexpressed the cellular factor shiftless (SFL), which blocks −1PRF of human immunodeficiency virus 1 (HIV) and SARS-CoV-2 [18,19,20,21], and a splice variant of SFL, termed SFL short (SFLS), which is unable to block −1PRF in the context of HIV infection [18].