The closely related Drosophila sry p and sry 6 zinc finger proteins show differential embryonic expression and distinct patterns of binding sites on polytene chromosomes

Serendipity (sry) beta (fi) and delta (5) are two finger protein genes resulting from a duplication event. Comparison of their respective protein products shows interspersed blocks of conserved and divergent amino-acid sequences. The most extensively conserved region corresponds to the predicted DNA-binding domain which includes 6 contiguous fingers; no significant sequence conservation is found upstream and downstream of the protein-coding region. We have analysed the evolutionary divergence of the sry ft and d proteins on two separate levels, their embryonic pattern of expression and their DNA-binding properties in vitro and in vivo. By using specific antibodies and transformant lines containing /3-galactosidase fusion genes, we show that the sry ft and sry S proteins are maternally inherited and present in embryonic nuclei at the onset of zygotic transcription, suggesting that they are transcription factors involved in this process. Zygotic synthesis of the sry /? protein starts during nuclear division cycles 12—13, prior to cellularLsation of the blastoderm, while the zygotic sry d protein is not detectable before germ band extension (stage 10 embryos). Contrary to sry 6, the zygotic sry (J protein constitutes only a minor fraction of the total embryonic protein. The sry /} and 6 proteins made hi E. coli bind to DNA, with partly overlapping specificities. Then" in vivo patterns of binding to DNA, visualised by immunostaining polytene chromosomes, differ both in the number and position of their binding sites. Thus changes hi expression pattern and DNA-binding specificity have contributed to the evolution of the sry ff and 6 genes.