RPS19 depletion results in nuclear retention of pre-40S particles.(A) HeLa cells were transfected with different siRNAs, as indicated, and grown for 24 hours. The intracellular location of the 18S rRNA precursors was then analyzed by FISH using the 5′-ITS1 probe conjugated to Cy3. In rps19-1 siRNA-treated cells, accumulation of 18S rRNA precursors in the nucleoplasm is indicated by arrows; the inset shows the boxed region at higher magnification. Comparison is made with cells treated for 24 hours with 100 μg/mL cycloheximide. (B) Detection of fibrillarin, a nucleolar protein, by immunofluorescence. Cells were treated with cycloheximide or transfected with the rps19-1 siRNA as in panel A. “Control” indicates untreated cells.