Fig. 4. Isolation of late cytoplasmic 40S pre-ribosomes. The indicated TAP-tagged protein baits were isolated from yeast lysates by the TAP method, and eluates were separated on a 4–12% SDS–polyacrylamide gradient gel followed by Coomassie Blue staining. Bait proteins are indicated by open circles. Prominent co-purifying proteins were identified by mass spectrometry (see also Table II). Non-ribosomal factors of the pre-40S particels are labeled. As a marker for 90S pre-ribosomes, TAP-purified Noc4p was also loaded on the gel (see also Grandi et al., 2002). High molecular weight 90S factors are marked by asterisks. Putative contaminants in the preparations (indicated by diamonds) are (from top to bottom): Ssa1/2p, Ssb1/2p, Pab1p, eEF-1α, Rpl3p, Rpl4p and Escherichia coli matrix porin f.