Characterization and purification of messenger RNAs containing poly A in insect imaginal disks.

The presence of a fragment of polyA resistant to both T1 and p ribonucleases in mRNAs extracted from wing imaginal disks of an insect, Pieris brassicae, is reported. Its length was approximatively 150 nucleotides. PolyU sepharose affinity chromatography was subsequently used for purification of these polyA(+)mRNA molecules. Analyses on sucrose gradients showed a good recovery of poly(+)molecules characterized by their size (20-100 S) and a polydisperse pattern. These mRNAlike species represent 2-3 per cent of the total radioactivity incorporated into RNA in 3 hours of labeling. Sequential extractions were carried out to provide cytoplasmic RNA rich fractions (4 degrees C) and nuclear rich fractions (45 degrees C). When assayed for the presence of polyA(+)RNA, molecules extracted by these two sequential methods were found to be very similar in their polyA content.