Cap-binding protein complex from uninfected and poliovirus- infected HeLa cells

In poliovirus-infected cells, protein synthesis initiation factor recognition of m7GTP cap groups is impaired due to a defect in the cap-binding protein complex (CBPC). To elucidate the specific structural and functional defects of this complex, the CBPC was purified from uninfected and poliovirus-infected HeLa cells. Structural analyses demonstrated that the CBPC from uninfected HeLa cells consisted of a tightly associated p24/p220 polypeptide core which co-purified with minor amounts of other polypeptides. Similar purification schemes applied to poliovirus-infected cell extracts produced a modified complex: the p220 component was absent, and antigenically related degradation products (100-130 kDa) co-purified with the p24 component. The association of polypeptides in the modified complex was found to be labile compared with those in the unmodified CBPC. In contrast to the drastic alteration of the p220 component following poliovirus infection, the p24 polypeptide was qualitatively and quantitatively unaltered as determined by two-dimensional electrophoresis. Preliminary functional studies suggested that p220 plays a role in enhancing the affinity with which the p24 subunit bindsto m7GTP cap groups. These studies also suggested that modified CBPC from poliovirus-infected cells may bind to cap groups with a reduced affinity as compared with the cap-binding affinity of unmodified CBPC from uninfected cells.