EXPRESSION AND BIOCHEMICAL ANALYSES OF THE RECOMBINANT POTATO-VIRUS-X25K MOVEMENT PROTEIN

The 25K movement protein (MP) of potato virus X (PVX) is encoded by th e 5'-proximal gene of three overlapping MP genes forming a 'triple gen e block'. The PVX 25K MP (putative NTPase-helicase) has been synthesiz ed in Escherichia coli as a recombinant containing a six-histidine tag at the amino terminus. The His-tagged 25K protein was purified in a o ne-column Ni-chelate affinity chromatography procedure. In the absence of any other viral factors, this protein had obvious Mg2+-dependent A TPase activity, which was stimulated slightly (1.7-1.9-fold) by variou s polynucleotides. Like other viral proteins possessing ATPase-helicas e motifs and many plant viral movement proteins, the PVX 25K MP was ab le to bind nucleic acids in vitro. The RNA binding activity of the 25K MP was pronounced only at very low salt concentrations and was indepe ndent of its ATPase activity.