Highly efficient β globin transcription in the absence of both a viral enhancer and erythroid factors

We have studied the transcription of the Xenopus major adult beta globin gene in microinjected Xenopus oocytes at various levels of injected template, with or without the SV40 enhancer. We find that enhancer-independent transcription is highly efficient, being only two orders of magnitude below the calculated in vivo rate. Linkage to the SV40 enhancer has very little stimulatory effect. We have also tested the effect of replication on transcription in the oocyte system where replication was induced by progesterone treatment followed by prick activation. We found that the presence of replicated templates did not stimulate expression of the Xenopus beta globin gene either in the presence or absence of the SV40 enhancer. In addition, we found that specificity of transcription, in cryptic of initiation at the cap site versus initiation at cryptic promoters upstream of the cap site, was dramatically improved by the injection of higher numbers of beta globin templates, by oocyte maturation and activation or by the presence of the SV40 enhancer.