INTERSPECIFIC COMPARISON OF DROSOPHILA SERENDIPITY-DELTA AND SERENDIPITY-BETA - MULTIMODULAR STRUCTURE OF THESE C2H2 ZINC-FINGER PROTEINS

The Drosophila serendipity (sry) beta and delta genes, which resulted from a gene duplication event, provide an interesting model for the ev olutionary diversification in structure and function of C2H2 zinc fing er proteins. We examined here the divergence of the sry beta and delta proteins over an estimated period of 45 million years by comparing th eir predicted sequences in D. melanogaster, D. pseudoobscura, and D. s ubobscura. Between orthologs, i.e., pairs of either sry beta or sry de lta, the NH2-proximal region delineated by pairs of C-X2-C motifs and the DNA-binding finger domain are highly conserved. Sequence conservat ion operates over the entire finger domain, including the links separa ting adjacent fingers, even though each has a unique sequence differen t from the widespread TGEKP motif. In contrast, the sequence of the ce ntral acidic region has extensively diverged and differs between speci es in the number of amino acids, probably because of slippage-driven m utations. The NH2-terminal region and fingers 1, 5, and 6 differentiat e the sry beta and delta proteins while zinc fingers 2, 3, and 4 are v irtually identical in these two paralogs. A nuclear localization signa l of the SV40T antigen type, preceded by a potential CKII phosphorylat ion regulatory site, is conserved in sry delta but not found in sry be ta. The interspecific conserved regions correlate well with the positi ons of zygotic lethal mutations in the D. melanogaster sry delta prote in. Furthermore, P-element transformation experiments show that a tran sgenic copy of the D. pseudoobscura sry delta gene rescues the sry del ta mutant phenotype. Convergence of genetic and structural data on the sry proteins supports a multimodular function and mode of evolution o f these C2H2 finger proteins.