MYCOPLASMA CONTAMINATION OF CELL CULTURES - INTERFERENCE WITH 32P-LABELLING PATTERN OF RNA

32P-labelled RNA was isolated from stable cell lines by a SDS -hot phenol procedure and fractionated by electrophoresis on agar gel. Apart from the RNA components typical of mammalian cells, two additional RNA fractions were detected with approximate S values of 16S and 23S. These fractions represented only a very small portion of the total cellular RNA, but had a high incorporation rate and a G+C A+U ratio of about 1. Microbiological, electron microscopical and biochemical studies proved that these fractions originated from mycoplasma contaminants. After treatment of the cultures with Tylan the microbiological tests for detection of mycoplasma became negative but the labelling of the 16S and 23S RNA fractions still persisted. Thus the 32P-labelling combined with fractionation of RNA on agar gel may be used as a very sensitive, although unspecific method for detection of mycoplasma in cell cultures. These studies emphasize the serious danger which the mycoplasma contamination represents when cell cultures are used for studies of RNA metabolism. © 1969.