Using a DNA probe from an avian transforming virus, NK24, that contains the fos gene and that was newly isolated and characterized (M. Nishizawa, N. Goto, and S. Kawai, J. Virol. 61:3733-3740, 1987), we cloned and sequenced the chicken c-fos gene. Results showed that this gene, like the mouse or human c-fos gene, contains four exons encoding a predicted gene product of 367 amino acids which is about 79% homologous to p55c-fos (mouse), excluding several small insertions or gaps. The predicted gene product, however, contains two nonhomologous regions, as suggested by sequence analysis of the NK24 genome. About half the identical amino acids of these gene products are encoded by different codons, and the guanine-plus-cytosine content in the third letter of each codon used in the entire chicken c-fos coding region is high (93%). The 5'-flanking region of the TATA box contains a sequence that is homologous to a putative transcriptional regulatory sequence in the mouse or human c-fos gene. The 3'-noncoding region of chicken c-fos is strikingly homologous to that of mouse or human c-fos and covers a 67-base-pair adenine-plus-thymine-rich stretch which was previously reported to be essential for an inhibitory effect on the expression of the mouse c-fos gene.
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