In Xenopus laevis, the gene encoding the elongation factor 1-α variant EF-1αO, where O stands for oocyte, is expressed in oocytes and early embryos. A genomic library from X. laevis was screened with a cDNA probe coding for EF-1αO. Two recombinant phages were isolated, one of which carries an entire EF-1αO gene. This clone was characterized by restriction enzyme mapping and sequencing. Comparison of cDNA and genomic sequences revealed that EF-1αO gene, as all locations of the splice junctions are conserved between the two genes. The sequence immediately upstream from the transcription start point (tsp) contains a CCAAT box, but does not contain either a TATA box or a Sp1-binding site. Interestingly, this sequence has a sequence homologous to the negative regulatory element from the TFIIIA promoter. A region located about 400 bp upstream from the tsp contains an additional number of possible regulatory sequence elements. The first intron contains G + C-rich elements which exist both isolated and as part of longer inverted repeats. Furthermore, one octamer and four Sp1-binding sites are found in this intron. © 1991.