FIG. 1.

Analysis of full-length R2 elements and their transcripts in D. simulans. (A) Diagram of an rRNA transcription unit with 18S, 5.8S, and 28S genes (black boxes), transcribed spacers (white boxes), and R2 insertion (gray box). R2 RNA transcripts are diagramed as processed from a cotranscript with the rRNA unit. Black bars above the DNA unit and the RNA cotranscript represent the products of PCR and RT-PCR assays, respectively, as shown in panel C. (B) Northern blot of total RNA from 12 D. simulans stocks probed with a fragment from the 5′ end of the R2 element. The arrow points to the full-length, 3,600-nt R2 transcript. The arrowhead points to the presumed 28S cotranscript discussed in the text. (C) A primer complementary to sequences within the R2 element was annealed to total RNA from the 12 stocks and used to prime reverse transcription by the M-MLV reverse transcriptase. The resulting cDNA was PCR amplified using an end-labeled 28S primer (80 nt upstream of the junction) and an R2 primer (108 nt downstream), and the products were separated on an 8 M urea, 7.5% polyacrylamide gel (left half). Genomic DNAs from each stock were directly amplified using the same PCR primers to reveal the lengths of R2 junctions present in each stock (right half). Arrows point to product lengths from the common R2 junction found in all stocks.