Transcriptional properties of chick embryonic erythroid nuclei in vitro.

Chick embryo red blood cells express the embryonic globin and the rRNA genes before 5 days of development but only the adult globin genes and no rRNA after 12 days of development. We have isolated nuclei from the red blood cells of these developmental stages and allowed them to transcribe in vitro. We have analyzed the overall transcriptional properties of these nuclei, the overall activities of RNA polymerases I and II and the sequence-specific activity of RNA polymerase II in the beta-globin domain using cloned genomic hybridization probes. Among our findings are the following. 1) Erythroid nuclei of 5-day embryos are more transcriptionally active than those at 12 days. 2) RNA polymerase I is a very active at 5 days but is off by 12 days. 3) A template-independent activity which yields labeled RNA is present in the red cell nuclei of 12-day but not 5-day embryos. 4) Between 5 and 12 days of development transcriptional modulation delineates embryonic and adult beta-globin domains. 5) These domains exceed the boundaries of the genes themselves by several kilobases. 6) All transcripts which hybridize to sequences in the beta-globin gene region, including repeat sequence transcripts, are transcribed by RNA polymerase II.