RESULTS
Purification ofRV 3' (+)-SL RNA Binding Protein. The RV 3'
(+)-SL RNA binding protein was fractionated from Vero 76
cells as described above. After fractionation of the binding
activity by rHPLC and SDS/PAGE, a major protein species of
=60 kDa was observed upon silver staining (Fig. 2A, lane 1).
Protein from the active rHPLC fraction (=100 ng) was incubated
with radiolabeled 3' (+)-SL RNA and UV irradiated to
induce covalent crosslinking. The radiolabeled RNA was associated
only with the 60-kDa protein, indicating it was the RNA
binding protein of interest (Fig. 2A, lane 2). To test the specificity
of the 60-kDa protein for the 3' (+)-SL RNA, we performed
an RNA gel retardation assay. The protein (=100 ng)
formed a specific complex with the 32P-labeled 3' (+)-SL RNA
(Fig. 2B, lane 1). A 25- to 75-fold molar excess of unlabeled 3'
(+)-SL RNA was sufficient to completely block the binding
activity (Fig. 2B, lanes 2 and 3, respectively). Similar concentrations
ofunrelated RNAs [globin and poly (I)-poly (C)] did not
affect the binding activity (data not shown). However, a large