Plaquelike Clearings Induced by Antimicrobial Agents on Lawns of Pseudomonas aeruginosa

Symmetrical in vivo transcription of mitochondrial DNA in HeLa cells

RNA.DNA hybridization experiments utilizing separated strands of HeLa mitochondrial DNA and mit-RNA from HeLa cells exposed to short pulses of [5-(3)H]uridine have shown that the labeled RNA hybridizes with both the light (L) and the heavy (H) strand, though to a different relative extent depending upon the labeling time. Thus, hybridization of pulse-labeled RNA is about equal with the two strands when the pulse is very short (1-5 min), and becomes more and more predominant with the H strand with increasing pulse length. Pulse-labeled fast-sedimenting mit-RNA forms RNase-resistant double-stranded structures up to more than 5 mum long when self-annealed or annealed with an excess of unlabeled mit-RNA. These observations and the previous evidence of complete transcription of the H strand strongly suggest that mit-DNA is transcribed in HeLa cells symmetrically over a considerable portion of its length, with the transcript of the L strand being rapidly degraded or otherwise removed from the mitochondrial fraction.