Table 1.
Estimates of total RNA content in mammalian cells.
| Type | Percent of total RNA by mass | Molecules per cell | Average size (kb) | Total weight picograms/cell | Notes | Reference |
|---|---|---|---|---|---|---|
| rRNAs | 80 to 90 | 3–10 × 106 (ribosomes) | 6.9 | 10 to 30 | Blobel and Potter (1967); Wolf and Schlessinger (1977), Duncan and Hershey (1983) | |
| tRNA | 10 to 15 | 3–10 × 107 | <0.1 | 1.5 to 5 | About 10 tRNA molecules /ribosome | Waldron and Lacroute (1975) |
| mRNA | 3 to 7 | 3–10 × 105 | 1.7 | 0.25 to 0.9 | Hastie and Bishop (1976); Carter et al. (2005) | |
| hnRNA (pre-mRNA) | 0.06 to 0.2 | 1–10 × 103 | 10* | 0.004 to 0.03 | Estimated at 2–4% of mRNA by weight | Mortazavi et al. (2008); Menet et al. (2012) |
| Circular RNA | 0.002 to 0.03 | 3–20 × 103 | ∼0.5 | 0.0007 to 0.005 | Estimated at 0.1–0.2% of mRNA** | Salzman et al. (2012); Guo et al. (2014) |
| snRNA | 0.02 to 0.3 | 1–5 × 105 | 0.1–0.2 | 0.008 to 0.04 | Kiss and Filipowicz (1992); Castle et al. (2010) | |
| snoRNA | 0.04 to 0.2 | 2–3 × 105 | 0.2 | 0.02 to 0.03 | Kiss and Filipowicz (1992); Cooper (2000), Castle et al. (2010) | |
| miRNA | 0.003 to 0.02 | 1–3 × 105 | 0.02 | 0.001 to 0.003 | About 105 molecules per 10 pg total RNA | Bissels et al. (2009) |
| 7SL | 0.01 to 0.2 | 3–20 × 104 | 0.3 | 0.005 to 0.03 | About 1–2 SRP molecules/100 ribosomes | Raue et al. (2007); Castle et al. (2010) |
| Xist | 0.0003 to 0.02 | 0.1–2 × 103 | 2.8 | 0.0001 to 0.003 | Buzin et al. (1994); Castle et al. (2010) | |
| Other lncRNA | 0.03 to 0.2 | 3–50 × 103 | 1 | 0.002 to 0.03 | Estimated at 1–4% of mRNA by weight | Mortazavi et al. (2008); Ramsköld et al. (2009), Menet et al. (2012) |
*The size for the average unspliced pre-mRNA is 17 kb; however, most pre-mRNAs are partially spliced at any given time, and the average size of hnRNA is estimated at 10 kb (Salditt-Georgieff et al., 1976).
**Based on the finding that 1–2% of all mRNA species generate circular RNA, which is present at 10% of the level of the parental mRNA.