ENCAPSIDATION OF TURNIP CRINKLE VIRUS IS DEFINED BY A SPECIFIC PACKAGING SIGNAL AND RNA SIZE

A protoplast infection assay has been used to reliably examine the vir al RNA encapsidation of turnip crinkle virus (TCV). Analysis of the en capsidation of various mutant viral RNAs revealed that a 186-nucleotid e (nt) region at the 3' end of the coat protein (CP) gene, with a bulg ed hairpin loop of 28 nt as its most essential element, was indispensa ble for TCV RNA encapsidation. When RNA fragments containing the 186-n t region were used to replace the CP gene of a different virus, tomato bushy stunt virus, the resulting chimeric viral RNAs were encapsidate d into TCV virions. Furthermore, analysis of the encapsidated chimeric RNA species established that the RNA size was an important determinan t of the TCV assembly process.