Transcription and RNA Processing Practice Test

In a eukaryotic cell, researchers isolate nuclear RNA from a gene containing three exons separated by two introns. A newly synthesized transcript is detected that hybridizes to probes complementary to exon 1, intron 1, exon 2, intron 2, and exon 3. After 10 minutes, the predominant nuclear RNA hybridizes only to exon probes, and sequencing shows exon 1 directly joined to exon 2 and exon 2 joined to exon 3. No changes are detected in the DNA sequence of the gene. Which explanation best accounts for the change in hybridization pattern over time?

An investigator compares nuclear RNA from two eukaryotic cell types and finds that both produce the same primary transcript from a gene with four exons. In cell type 1, the predominant processed RNA contains exons 1-2-3-4. In cell type 2, the predominant processed RNA contains exons 1-2-4, with exon 3 absent; splice junctions match known splice-site sequences. The DNA sequence of the gene is identical in both cell types. Which explanation best accounts for the different processed RNAs?