In D.melanogaster three ras genes were isolated and mapped to regions 85D, 64B and 62B, respectively (Neuman-Silberberg et al, 1984). Nucleotide sequence analysis of genomic and cDNA clones suggests that the putative Drosophila ras proteins have a molecular weight of 21 to 23 kd. They share on average 80 percent similarity with vertebrate ras p21 proteins at their N-terminus and 40 percent at their C-terminus. The specific pattern of sequence conservation is similar to that found when vertebrate ras genes are compared among themselves or with yeast ras genes, probabely reflecting different domains within the ras protein (Neuman-Silberberg et al, 1984; Mozer et al, 1985; Brock, 1987). Since the Drosophila rani. gene is more similar to vertebrate ras genes than to the Drosophila ras2 gene, it has been proposed that the two Drosophila genes have diverged anciently and that they have different functions (Brock, 1987). The structural and functional homologies between the Drosophila and vertebrate ras proteins were demonstrated by precipitating 21 and 27 to 28 kd proteins from Drosophila cell extract using monoclonal antibodies raised against the vHa-ras p21 protein (Papageorge et al, 1984), and by transforming rat cells with a chimeric ras comprising the N-terminus of human activated Ha-ras gene and the C-terminus of Drosophila ras gene (Schejter et al, 1985).
KeywordsTranscription Start Site Transcription Unit Ras2 Gene Bidirectional Promoter Large Transcript
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