Human globin gene transcription in injected Xenopus oocytes: enhancement by sodium butyrate

We have studied the expression of the human adult (beta) and foetal (gamma) globin genes by injecting a cosmid containing the complete -G gamma-A gamma-psi beta-delta-beta cluster into Xenopus oocytes. The transcripts from the gamma and beta genes were characterised with respect to their 5' termini by S1 nuclease mapping using probes which extend 5' to the cap site and 3' into the first exon. The only beta transcripts detectable in injected oocytes spanned from either -231 or -177 (cap site +1) into the first exon. The sensitivity of this transcription to inhibition by a low concentration of alpha-amanitin indicated that polymerase II was responsible. S1 analysis of gamma gene transcripts showed that the predominant transcript mapped from a site at -227, but a low level of transcription from the cap site was also detectable. Incubation of oocytes in saline solution containing sodium butyrate prior to injection resulted in a significant stimulation of transcription from the gamma gene cap site. In contrast, transcription from the beta gene upstream sites was only slightly increased. The possible role of sodium butyrate in promoting this effect is discussed in the context of its known property as a modifier of cellular chromatin.