| Comments |
P.8 left column 2nd paragraph: "Next, [investigators] investigated whether co-transcription on a single allele copy of γ- and β-globin was independent, treating all alleles as a pool irrespective of which cell they were in. This analysis required estimating the number of non-transcribing alleles in the population, which is not measurable by RNA FISH. [They] thus performed cell-cycle analysis of cultured human cells using RNA FISH: cells with histone 4 mRNA are in S-phase, cells without histone 4 mRNA with a small nucleus are in G1, while cells without histone RNA with a larger nucleus are in G2 (Padovan-
Merhar et al., 2015). Using this method, [they] found that 40% of cells were in G1, 31% in S, and 29% in G2 (Figure S5D). Since the β-globin locus is early replicating in erythroid cells (Goren et al., 2008), [they] conservatively assumed that each S and G2 cell had 4 copies, resulting in an average of 3.2 copies per cell (40% of 2 alleles + 60% of 4 alleles = 3.2 alleles). However, [they] also carried out calculations with different possible numbers of alleles: 2.6 alleles (which assumes that globin is replicated at the end of S phase) and 3 alleles (if globin is replicated near the middle of S) (Figures S5E and S5F)." |