Histidine-tagging and purification of tobacco etch potyvirus helper component protein.

The coding sequence for a series of six histidines (his-tag) was inserted near the 5' terminus of the helper component (HC) coding region of tobacco etch potyvirus (TEV). Full length genomic clones containing the his-tag coding sequence were infectious and produced symptoms in tobacco (Nicotiana tabacuma) similar to those induced by wild-type TEV. The modified virus was genetically stable and the his-tag sequence was maintained through at least four cycles of aphid transmission. A protocol for purifying rapidly the HC protein, based on the affinity of its his-tag for Ni(2+)-charged resin, yielded large amounts of his-tagged HC protein that was fully functional as demonstrated by aphid transmission experiments.