“…This RNA species has properties very similar to those of rapidly-labelled RNA of hydrated plant tissues described variously as polydisperse, heterogeneous, messengerlike and D RNA (see Loening, 1968) and is probably equivalent to the heterogeneous nuclear (Hn) RNA of animal tissues (Naora, 1973). Hn RNA is synthesized in the main body of the nucleus, has a short half-life, and most of it is broken down in situ (Attardi, Parnas, Hwang & Attardi, 1966;Soeiro, Vaughan, Warner & Darnell, 1968).…”