A Comparative study of RNA synthesis in liver cells functioning at different levels of organisation

K S N PRASAD & P M BHARGAVA

Centre for Cellular and Molecular Biology Hyderabad, 500007, A.P., India

Published in: Indian Journal of Biochemistry & Biophysics, 1982, 19, 75-85.

A comparative study of RNA labelled by [32P] phosphate in dispersed liver parenchymal cells and liver slices in vitro, and in whole liver in vivo, has been carried out. Dispersed liver cells incorporated [31P] phosphate into RNA linearly for at least up to 4 hr. In cells labelled with [12P]phosphate for 2 hr in vitro, high-molecular weight ( > 28S)-RNA accounted for 40-50% of the label; mature rR.NA, ~10%; 4-5S RNA, ~14%; and the other RNAs, 26-36%. Poly (A)-containing RNA constituted 20-30% of the total cellular RNA labelled at 1-2 hr in dispersed liver cells. As indicated by the G+C content, only a small proportion ( <25%) of the radioactivity in the high-molecular weight ( > 28S)-RNA synthesised at 2 hr by dispersed liver cells represented labelling of pre-rRNA; much of the high-molecular weight(> 28S)-RNA was found to undergo degradation, some of it to 4-5S fragments, on chasing with actinomycin D for 2 hr. Using sensitivity to actinomycin D as the criterion, RNA labelled at 1-2 hr in dispersed liver cells could be classified into three classes: Class 1 constituting 50-60%. Class 2 constituting 20-25%, and Class 3 constituting ~15%, of the total label, the synthesis of which was inhibited at actinomycin D concentrations of 0.02-0.03, 0.05- 0.1, and 0.2-0.5 μg/ml, respectively. No significant differences were found between dispersed liver cells and liver slices in regard to the nature of RNA synthesised at any time point between 0.5 and 5 hr. Dispersed liver cells and liver slices in vitro did not differ from whole liver in vivo in regard to the rate of labelling of 4-5S RNA. However, at any given time, the proportion of radioactivity in the I8S and 28S rRNAs was much less, while that in the high-molecular weight(> 28S)-RNA was more, in the case of dispersed liver cells and liver slices in vitro than in whole liver in vivo. This difference may be due to hormonal regulation of liver rRNA synthesis and loss of this regulation on killing the animal and excising the tissue. The relevance of the above observations to the difficulty experienced earlier in growing dispersed liver cells in vitro is discussed.

PMID:6182092

Keywords:
Aging, Liver/growth & development, Liver/metabolism, RNA/biosynthesis, Transcription, Genetic

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A Comparative study of RNA synthesis in liver cells functioning at different levels of organisation. K S N PRASAD & P M BHARGAVA. Indian Journal of Biochemistry & Biophysics, 1982, 19, 75-85.

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