Table 3.

Cellular levels of Upf1p, Nmd2p, and Upf3pa

Protein or ribosomesProtein
No. of molecules per cell% Soluble
Upf1p1,6000.007
Nmd2p1600.0007
Upf3p800.00035
Sup45p29,600b 0.2b
Xrn1p29,000c 0.2c
Ribosomes300,000d 7
  • a The relative abundance of Upf1p and Nmd2p was determined by comparing Western blot band intensities of theUPF/NMD factors present in crude cell extracts to those of the individual proteins. For Upf1p and Nmd2p, highly purified recombinant GST-Upf1p and GST-Nmd2p were used as standards, respectively. For Upf3p, cells bearing an HA-NMD2 allele were used as the standard. Calculations used to derive protein abundance are summarized in Materials and Methods.

  • b Cellular Sup45p levels determined by Gygi et al. (16).

  • c Cellular Xrn1p levels determined by Heyer et al. (25).

  • d Cellular levels of ribosomes determined by Waldron and Lacroute (56).