Apparent absence of symmetrical transcription in Tetrahymena mitochondria

Transcription in Tetrahymena pyriformis mitochondria has been examined for whether or not symmetrical transcription occurs. A ribonuclease A digestion in high-ionic strength was used as a test for the presence of double-stranded RNA (dsRNA) either before or after self-annealing. This test was applied to RNA prepared using pulse lengths of from 1 to 30 min. If symmetrical transcription occurred, then the amount of dsRNA should have varied inversely with pulse length. There was no evidence for the presence of dsRNA other than a ribonuclease-resistant core. A search was also made among the largest transcripts present (greater than 26S) since this region of a sucrose gradient is enriched in symmetrical transcripts in HeLa cells. Again none were found. In order to allow for possible rapid processing as the reason for the failure to find dsRNA, total cellular RNA was extracted as quickly as possible, and the ribonuclease digest analyzed by Sephadex chromatography. No large pieces of dsRNA were found.