Molecular cloning and sequencing of OAX DNA: an abundant gene family transcribed and activated in Xenopus oocytes.

OAX DNA codes for a 181 nucleotide long RNA whose transcription is strongly activated in somatic nuclei after their injection into a Xenopus oocyte nucleus. OAX RNA can be transcribed in vitro using an extract of Xenopus oocyte nuclei and total genomic DNA. Hybridization with OAX RNA as a probe indicates that OAX DNA is abundant in the Xenopus genome (at least 10(4) copies per genome). OAX DNA is present in tandemly repeated HindIII units of 752 bp. The complete DNA sequence of one of these OAX HindIII units is reported here. The OAX RNA transcript has been mapped within the OAX HindIII unit using S1 nuclease. Microinjection into Xenopus oocyte nuclei of either the OAX HindIII unit or a subclone containing only the RNA coding portion of the OAX HindIII unit both produce OAX RNA transcripts. This shows that the OAX promoter lies within the coding region of the RNA. The OAX RNA sequence has two elements which fit the RNA polymerase III promoter consensus sequence, and shows homology with dispersed RNA polymerase III transcription units in mammals.