FIG. 5.

A reduction in YB-1 and p54nrb levels alters the association of c-myc mRNA with the polysomes. Cells were transfected with plasmids that reduce the expression of YB-1, p54nrb, or GRSF-1, and postnuclear extracts were separated on 10 to 55% sucrose density gradients. No overall changes in the polysome profiles were observed. RNA was generated from the individual fractions, and Northern analysis was performed using probes to c-myc and actin mRNA. When levels of YB-1 are reduced, there is a relocation of the c-myc mRNA from the polysomal region to the subpolysome particles (A). In cells with reduced expression of p54nrb, there is again a reduced polysomal location of c-myc mRNA (B), but no difference was observed in cells with a decreased expression of GRSF-1 (C). (D) To test the effect of the reduction in the levels of ITAFs on cell proliferation rates, the levels of these proteins were reduced as described above and cells were incubated with [³H]thymidine for 24 h and counted.