FIG. 3.

Pnn is associated with mRNPs in vivo. (A) A schematic diagram shows the intron-containing CAT reporter, pSV40-CAT(In1), and the experimental design for the RPA. Two RPA products of 347 and 223 nt correspond to unspliced and spliced mRNA, respectively. (B) Thirty-six hours after transfection with the reporter, cell lysates were prepared and then subjected to immunoprecipitation with mock (lane 3) or anti-Pnn (lane 4) antibodies. RPA with 5% total RNA prepared from transfected cells is shown in lane 2. Lane 1 is a lighter exposure of the autoradiogram of lane 2. Lane 5 shows RPA with in vitro-transcribed intron-lacking CAT RNA, indicating the size of protected spliced mRNA. The intensity of protected RNA fragments was measured using a PhosphorImager; the ratios of spliced to unspliced RNA in the input and anti-Pnn precipitate are shown, indicating preferential association of Pnn with spliced mRNPs.