Genetic organization of the c-sis transcription unit

The structure and genetic organization of the transcription unit of the c-sis proto-oncogene was determined. Comparative nucleotide sequence analysis of the exon sequences of feline and human c-sis revealed a very high degree of homology. The cap site as well as the poly(A)-addition site of the sis transcript of each species was identified and found in similar positions. An insert of 4 amino acids was found in the deduced translational product of feline c-sis and it was located at the amino-terminus of the region that constituted the platelet-derived growth factor domain. An insert of 149 bp present at the 5' end of exon 7 of human c-sis but absent in the simian sarcoma virus v-sis oncogene was also present in the feline c-sis proto-oncogene.