Intact and consistent protein biosynthesis relies on the ability of the ribosome to stay in the correct open reading frame (ORF) during translation. When the ribosome fails to maintain the proper ORF, translation usually results in either incorrect protein synthesis or early termination as a result of the introduction of a premature stop codon. However, a shift in the ORF is not universally deleterious, as many viruses capitalize on this phenomenon by using a programmed ribosomal frameshift (PRF) to translate several proteins from the same sequence, thereby maximizing the storage capacity of their genome. Thus, many viruses (including HIV-1) are categorized as having a polycistronic genome, meaning they employ multiple active ORF's in a single gene.