Control of rRNA Production in Non-growing Cells

Abstract

EMERSON reported that the rate of rRNA production in contact-inhibited chick skin fibroblasts was lower than that in growing cells¹ and attributed this to prolongation of 45S RNA transcription time during contact inhibition. In support of this conclusion, he showed that in contact-inhibited cells, with relatively short labelling times, there was a deficiency in the amount of radioactivity appearing in 18S rRNA relative to that found in 28S rRNA. This would result from prolonged 45S transcription time if a significant number of the 45S precursor molecules converted to 28S and 18S rRNAs during the short labelling period were labelled only in their distal (3′-OH) end, having been in mid-transcription when labelling was begun. If the 28S segment of the 45S precursor lies closer to the 3′-OH terminus than the 18S segment, the latter would receive relatively less label.