The polysome-associated proteins Scp160 and Bfr1 prevent P body formation under normal growth conditions

Numerous mRNAs are degraded in processing bodies (P bodies) in S. cerevisiae. In logarithmically growing cells only 0-1 P bodies per cell are detectable. However, the number and appearance of P bodies change once the cell encounters stress. The polysome-associated mRNA binding protein Scp160 interacts with P body components such as the decapping protein Dcp2 and the scaffold protein Pat1, presumably on polysomes. Loss of either Scp160 or its interaction partner Bfr1 caused the formation of Dcp2-positive structures. These Dcp2-positive foci contained mRNA, since their formation was inhibited by the presence of cycloheximide. In addition, Scp160 was required for proper P body formation because only a subset of bona fide P body components could assemble into the Dcp2-positive foci in Δscp160 cells. In either Δbfr1 or Δscp160, P body formation was uncoupled from translational attenuation as the polysome profile remained unchanged. Collectively, our data suggest that Bfr1 and Scp160 prevent P body formation under normal growth conditions.