Viral Infection and Immunoprecipitation of 32P-Labeled
Calreticulin from Cell Extracts. Vero 76 cells were infected
with RV M33 strain as described (5). Approximately 5 x 106
infected and uninfected cells were grown in 100-mm dishes in
Dulbecco's modified Eagle's medium, incubated for 2 hr with
[32P]orthophosphoric acid (New England Nuclear) at 0.5
mCi/ml (specific activity =8000 Ci/mmol; 1 Ci = 37 GBq) in
phosphate-free medium. Cells were lysed with NET buffer
(10 mM Tris-HCl, pH 7.4/150 mM NaCl/0.1% Triton X-100)
containing phosphatase inhibitors (1 mM sodium orthovanadate/
G.1 AM okadaic acid), in addition to protease inhibitors
[25 AM p-nitrophenyl p'-guanidinobenzoate/leupeptin (10
,ug/ml)]. Preparation of cytolysate and immunoprecipitation
of calreticulin was performed as described (7).