The drosophila ras oncogenes: Structure and nucleotide sequence

Three Drosophila genes homologous to the Ha-ras probe were isolated and mapped to positions 85D, 64B, and 62B on chromosome 3. Two of these genes (termed Dras1 and Dras2) were sequenced. In the case of Dras1, which contains multiple introns, a cDNA clone was isolated and sequenced. In the case of Dras2, the nucleotide sequence of the genomic clone was determined. Each gene codes for a protein with a predicted molecular weight of 21.6 kd. Alignment of the amino acid sequence of Dras1 with the vertebrate Ha-ras protein shows that at the amino terminus and central portion (residues 1-121 and 137-164) the two proteins are remarkably similar, and have an overall homology of 75%. The Dras2 gene lacks significant homology to the vertebrate counterpart at the extreme amino terminus and is homologous only between positions 28-120 and 139-161 (overall homology of 50%). This result suggests that the N terminus of p21 forms a distinct regulatory or functional domain. At the carboxy terminus, the major region of variability among the vertebrate ras proteins, the two Drosophila sequences also display considerable variability. However, both appear to be more similar to exon 4B of the Ki-ras gene.