Figure 2.

Depletion of B-factors causes few changes in the SDS–PAGE profile of proteins contained in pre-ribosomes. Nine of the 12 B-factors necessary for processing of 27SB pre-rRNA were individually depleted using the conditional GAL promoter. TAP-tagged ribosome assembly factor Nop7 was used to purify 90S and 66S pre-ribosomes from yeast grown in YEPGal (left lane in each pair), and from strains grown in YEPGal and shifted to YEPGlu for 16 h to deplete each B-factor (right lane in each pair). Proteins present in purified pre-ribosomes were separated by SDS–PAGE and stained with silver. TAP-tagged Rpf2 was used to purify pre-ribosomes from the GAL-RLP7 strain in which Rlp7 was depleted. Rlp7 is required for processing of 27SA₃ pre-rRNA. Thus, this strain serves as a control to demonstrate specificity of the gel profiles for B-factor-depleted strains. Silver-stained bands that increased in the absence of each assembly factor are indicated with solid circles. Bands that decreased are indicated with hollow circles. When able to be identified, the protein under control of the GAL promoter is indicated with #.