FIGURE 6.

Aminoacyl-tRNA synthetases cosediment with ribosomes. A, polysome profile of HeLa cells. Polysomes from exponentially growing HeLa cells were subjected to sucrose gradient centrifugation. A₂₅₄ was recorded, and the fractions were analyzed by Western blotting (WB) with antibodies directed to MetRS, LysRS, ArgRS, p43, p38, and p18 from MARS, or to EF1Bβ from the ValRS-EF1 complex. B, extracts of HeLa cells were subjected to low speed (10,000 × g) or high speed (100,000 × g) centrifugation, and the supernatants and pellets were analyzed by Western blotting, as indicated. HeLa cells growing in a p38^si or p43^si background were also analyzed in parallel.