Comparison of nucleotide sequence data of the 5' region of a fes/fps viral oncogene with those of the v-fes/fps homologous regions of man and cat revealed the position of the 3' portion of an as yet unidentified c-fes/fps exon. Comparative Southern blot and heteroduplex analysis of human and feline DNA immediately upstream of the v-fes/fps homologous regions showed extensive but discontinuous homology over a 9 kbp DNA stretch, which we have designated as fur. Northern blot analysis of mRNA from KG-1 myeloid cells with fes/fps- or fur-specific probes revealed a 3.0 kb fes/fps and a 4.5 kb fur transcript. Analysis of a number of tissues of an adult Wistar Lewis rat for the presence of fur transcripts revealed its differential expression pattern. An 0.95 kbp fes/fps-related and a 2.2 kbp fur-related cDNA recombinant clone were isolated from an oligo(dT)-primed KG-1 cDNA library. Comparative nucleotide sequence analysis of the fes/fps cDNA and its human genomic counterpart indicated that the cDNA contained genetic sequences that were identical to and colinear with exon 15-19 and, furthermore, that the poly(A) addition signal near the 3' end of exon 19 was functional. Similar analysis of the 2.2 kbp fur cDNA indicated that the poly(A) addition signal of the fur transcript was in close proximity of the newly discovered fes/fps exon. The region in between contained a CATT sequence but no 'TATA' box. The fur transcript was characterized by a long noncoding region at its 3' end.