Cloning and expression of chicken p54c-ets cDNAs: the first p54c-ets coding exon is located into the 40.0 kbp genomic domain unrelated to v-ets.

We have isolated cDNA clones of chicken c-ets mRNA the longest of which, designated pCk E54A, contained approximately 2.0 kb of a c-ets mRNA species. Nucleotide sequencing of this clone revealed a single long open reading frame, extending from the first ATG codon (nucleotide +1) to a TGA termination codon at nucleotide 1324. The predicted translation product contains 441 amino acid residues and its molecular weight is 48 kd. Expression in COS-1 cells of this clone resulted in the synthesis of polypeptides immunologically indistinguishable from the authentic p54c-ets after one-dimensional gel electrophoresis. Comparison of the nucleotide sequence of this cDNA to that of v-ets of avian acute leukemia virus E26 showed that both sequences are almost colinear with the exception of five point mutations but present striking differences in their 5' and 3' parts. 79 nucleotides downstream of the first ATG codon in c-ets cDNA are not found in the 5' part of v-ets where they are replaced by 223 different nucleotides. The 3' parts of v-ets and the coding region of the chicken c-ets cDNAs are also different: the last 13 codons of the cDNA are replaced by 16 different codons in v-ets. Thus our results precisely define the structural differences between the ets encoded domain of E26 viral transforming protein (P135 gag-myb-ets) and the normal cellular protein p54c-ets expressed at high levels in chicken thymocytes and bursal lymphocytes. They also suggest the possibility of alternative splicing of different 5' exons to a common set of 3' exons.