A retrocopy of a gene can functionally displace the source gene in evolution

The e(y)2 gene of Drosophila melanogaster encodes the ubiquitous evolutionarily conserved co-activator of RNA polymerase II that is involved in transcription regulation of a high number of genes. The Drosophila e(y)2b gene, paralogue of the e(y)2 has been found. The analysis of structure of the e(y)2, e(y)2b and its orthologues from other species reveals that the e(y)2 gene derived as a result of retroposition of the e(y)2b during Drosophila evolution. The mRNA-derived retrogenes lack introns or regulatory regions; most of them become pseudogenes whereas some acquire tissue-specific functions. Here we describe the different situation: the e(y)2 retrogene performs the general function and is ubiquitously expressed, while the source gene is functional only in a small group of male germ cells. This must have resulted from retroposition into a transcriptionally favorable region of the genome

Expression pattern of dd4, a sole member of the d4 family of transcription factors in Drosophila melanogaster

In vertebrates, three members of the d4 gene family code for proteins, which are believed to function as transcription factors and involved in regulation of various intracellular processes. One member of the family, ubi-d4/requiem is ubiquitously expressed gene and two other, neuro-d4 and cer-d4, are expressed predominantly in the neural tissues (Nucleic Acids Res. 20 (1992) 5579; Biochim. Biophys. Acta 14 (1992) 172; Mamm. Genome 11 (2000) 72; Mamm. Genome 12 (2001) 862). Typically, d4 proteins show distinct domain organisation with domain 2/3 in the N-terminal, Krüppel-type zinc finger in the central and two adjacent PHD-fingers (d4-domain) in the C-terminal part of the molecule. However, alternative splicing, which is responsible for complex expression patterns of both neurospecific members of the family, generates multiple protein isoforms lacking certain domains (Nucleic Acids Res. 20 (1992) 5579; Genomics 36 (1996) 174; Mamm. Genome 11 (2000) 72; Mamm. Genome 12 (2001) 862). Exact function of d4 proteins is unclear but their involvement in regulation of differentiation and apoptotic cell death has been proposed (J. Biol. Chem. 269 (1994) 29515; Mamm. Genome 11 (2000) 72; Mamm. Genome 12 (2001) 862). Here we identified a single gene, dd4, in the genome of Drosophila melanogaster, the protein product of which could be assigned to the d4 family. Expression of dd4 is regulated during Drosophila development, and is most prominent in syncytial embryos and later in the embryonic nervous and reproductive systems. In flies dd4 mRNA is found in most tissues but the highest level of expression is detected in ovaries

Two Different Drosophila ADA2 Homologues Are Present in Distinct GCN5 Histone Acetyltransferase-Containing Complexes

We have isolated a novel Drosophila (d) gene coding for two distinct proteins via alternative splicing: a homologue of the yeast adaptor protein ADA2, dADA2a, and a subunit of RNA polymerase II (Pol II), dRPB4. Moreover, we have identified another gene in the Drosophila genome encoding a second ADA2 homologue (dADA2b). The two dADA2 homologues, as well as many putative ADA2 homologues from different species, all contain, in addition to the ZZ and SANT domains, several evolutionarily conserved domains. The dada2a/rpb4 and dada2b genes are differentially expressed at various stages of Drosophila development. Both dADA2a and dADA2b interacted with the GCN5 histone acetyltransferase (HAT) in a yeast two-hybrid assay, and dADA2b, but not dADA2a, also interacted with Drosophila ADA3. Both dADA2s further potentiate transcriptional activation in insect and mammalian cells. Antibodies raised either against dADA2a or dADA2b both immunoprecipitated GCN5 as well as several Drosophila TATA binding protein-associated factors (TAFs). Moreover, following glycerol gradient sedimentation or chromatographic purification combined with gel filtration of Drosophila nuclear extracts, dADA2a and dGCN5 were detected in fractions with an apparent molecular mass of about 0.8 MDa whereas dADA2b was found in fractions corresponding to masses of at least 2 MDa, together with GCN5 and several Drosophila TAFs. Furthermore, in vivo the two dADA2 proteins showed different localizations on polytene X chromosomes. These results, taken together, suggest that the two Drosophila ADA2 homologues are present in distinct GCN5-containing HAT complexes