MATERIALS AND METHODS
Protein Purification. Approximately 4 x 1010 cells were
grown to confluence in roller bottles, and cell lysates were
prepared as described (5). The supernatant was loaded onto a
QAE Sephadex column equilibrated with 10 mM Tris HCl (pH
7.4). The column was extensively washed with the equilibrating
buffer, and the RNA binding protein was eluted with a NaCl
gradient of 0-1.5 M in 500 ml. The presence ofthe RNAbinding
protein in the chromatography fractions was monitored by
RNA gel-shift assay with a radiolabeled synthetic RNA representing
the RV 3' (+)-SL sequence (Fig. 1) transcribed from a
DNA template as described (5). The active fractions were
pooled, concentrated in the presence of polyethylene glycol
(Mr, 20,000), and dialyzed overnight against 10 mM Tris HCl
(pH 7.4).