SunTag(v1) is a 22 residue peptide (LLPKNYHLENEVARLKKLVGER) that is bound robustly and specifically by the scFv(GCN4) single-chain variable fragment antibody (PMID:25307933). SunTag(v1) is a modified version of a scFv(GCN4) compatible epitope originally derived (PMID:10644744) from the Saccharomyces cerevisiae GCN4 gene ( SGDID:S000000735 ). If a protein of interest is tagged with a repeating array of the SunTag(v1) epitope, multiple copies of scFv(GCN4) can be recruited to the SunTag(v1) array. This property of 'signal amplification via protein multimerization' can be used to visualize expression of the SunTag(v1) array-tagged protein of interest, if for example the scFv(GCN4) antibody sequence is fused to a fluorescent protein. Arrays of SunTag(v1) are expressed at extremely low levels in cells, likely due to protein instability of the repeated array, and thus this tag is most useful for single-molecule imaging (PMID:25307933).