Genome Res. 2012 Oct;22(10):2031-42. doi: 10.1101/gr.131847.111.

Windhager L, Bonfert T, Burger K, Ruzsics Z, Krebs S, Kaufmann S, Malterer G, L'hernault A, Schilhabel M, Schreiber S, Rosenstiel P, Zimmer R, Eick D, Friedel CC, Dölken L.

Ultrashort and progressive 4sU-tagging reveals key characteristics of RNA processing at nucleotide resolution.

60/5 min ratios “were highest for introns in a range of 300–400 nt”.