The function of SHFL (shiftless antiviral inhibitor of ribosomal frameshifting, Ensembl gene identifier ENSG00000130813) is as follows. Inhibits programmed -1 ribosomal frameshifting (-1PRF) of a variety of mRNAs from viruses, such as HIV1, and cellular genes, such as PEG10. Interacts with the -1PRF signal of target mRNA and translating ribosomes and causes premature translation termination at the frameshifting site (PubMed:30682371). Regulates HIV1 GAG-POL expression by inhibiting -1PRF (PubMed:30682371). Exhibits antiviral activity against dengue virus (DENV) and can inhibit the replication of all DENV serotypes. May block the protein translation of DENV RNA via its association with cellular mRNA-binding proteins and viral RNA. Also interrupts Zika virus replication by promoting viral NS3 degradation via a lysosome-dependent pathway (PubMed:32150556). Can also limit the replication of hepatitis C virus (HCV) by restricting formation of viral replication organelle, West Nile virus (WNV), Chikungunya virus (CHIKV), herpes simplex virus type 1 (HHV-1), herpes virus type 8 (HHV- 8) and human adenovirus (PubMed:26735137, PubMed:27974568, PubMed:30944177, PubMed:32294532). Binds nucleic acids with a higher affinity for ssRNA and ssDNA than for dsDNA (PubMed:27974568). {ECO:0000269|PubMed:26735137, ECO:0000269|PubMed:27974568, ECO:0000269|PubMed:30682371, ECO:0000269|PubMed:30944177, ECO:0000269|PubMed:32150556, ECO:0000269|PubMed:32294532}. Isoform 4 does not inhibit programmed ribosomal frameshifting (-1PRF). Does not bind to ribosomes. .