A cDNA library (a gift of Dr. D. Melton, Harvard University) prepared from X. laevis oocyte RNA was screened with avian virus E26 v-ets DNA as a probe. From one million plaques, 23 positive clones were obtained. One of these contained a 2.5 kb DNA insert. The DNA sequence of this clone, as determined by the dideoxynucleotide chain termination method, was found to contain a single major open reading frame capable of coding for at least 467 amino acid residues. Since it is more closely related to c- ets-2 sequences from human, mouse, and chicken than to c-ets-1 or v-ets sequences, this cDNA is derived from a transcript of the X. laevis c-ets-2 gene. The open reading frame begins at the extreme 5'-end of the clone with homology starting at residue 6 of the other ets-2 genes. The X. laevis ets-2 sequence contains extensive homology with the ets-2 sequences throughout its length and it is coterminal with these c.ets-2 sequences. The methods for fertilization in vitro, and the isolation of RNA and proteins from different staged oocytes, have been established. The pattern of RNA expression of the c-ets-2 gene in X. laevis was examined by RNA gel blot analysis of RNAs from oocytes and embryos at different stages of development. For each stage, a single 3.2 kb mRNA species was observed. The maximum level of expression was found in the early stage oocytes.
