||Jackson DA, Pombo A, Iborra F. The balance sheet for transcription: an analysis of nuclear RNA metabolism in mammalian cells. FASEB J. 2000 Feb14(2):242-54. p.243 left column 2nd paragraphPubMed ID10657981
|| Greenberg, H., and Penman, S. (1966) Methylation and processing of ribosomal RNA in HeLa cells. J. Mol. Biol. 21, 527–535  Emerson, C. P., Jr. (1971) Regulation of the synthesis and the stability of ribosomal RNA during contact inhibition of growth. Nature (London) New Biol. 232, 101–106PubMed ID19768869, 5284943
||P.243 left column 2nd paragraph: "In a HeLa cell, 120–150 active rRNA genes
(ref 20 Jackson et al., 1998 PMID 9614191) are each associated with 100–120 transcription complexes (ref 19 Miller et al. 1972 PMID 4562652). With a synthetic rate of ~2.5 kbp/min (primary sources 21, 22), this is sufficient to yield 4×10^6 complete transcripts/22h cell cycle and maintain the observed steady-state level of ~3.5×10^6 ribosomes in these proliferative cells (ref 23)." Primary sources 21 & 22 study HeLa cells & chick skin fibroblasts, respectively.