Rapidly labelled RNA in heterotrophically cultured tissues of Nicotiana tabacum

Abstract

The RNA metabolism in tissue cultures of Nicotiana tabacum has been studied by incorporation of radioactive phosphate. The RNA was extracted by phenol-kresol-hydroxychinon and fractionated by MAK columns. A rapidly labelled RNA fraction was eluted from the MAK column after the rRNA components. Its base ratio differed from the latter in that the AMP content (28,6%) was higher than the GMP content (26,0%). Sedimentation analysis on sucrose gradients showed a sedimentation coefficient of 37 -38s. The life time of the 37-38s RNA fraction in chase experiments was 3,5-4 hours. Differential centrifugation of tissue homogenates revealed that the labelled 37-38s RNA was associated with particles sedimented by low speed centrifugation. No 37-38s RNA could be detected in the ribosomal fraction and the supernatant. During chase experiments label appeared in the rRNA components. It could be excluded by thin layer chromatographic separation of 32P labelled compounds that this label originated from 32P-o-phosphate or labelled organic phosphates except of the rapidly labelled 37-38s RNA. From this it was concluded that the 37-38s RNA is a precursor of the rRNA.