Modulo, a new maternally expressed Drosophila gene encodes a DNA-binding protein with distinct acidic and basic regions.

We have cloned, following an immunological screen of an expression library, five cDNA clones encoding the modulo antigen, a DNA-binding protein differentially expressed during Drosophila development. In addition a series of overlapping cDNA and genomic clones were also isolated. This protein is the product of a 2.2 kb mRNA that is encoded by a single genetic locus (100F). Analysis of the complete 544 amino-acid sequence, deduced from nucleotide sequence of cDNAs, shows that the polypeptide exhibits a primary structure with distinct charged regions, a modular structure found in several eukaryotic nuclear proteins, either transcription regulators or structural factors. The amino and carboxyl termini are rich in basic residues. The first third of the sequence contains a long domain comprised almost entirely of glutamic and aspartic acid residues. A typical cAMP dependent phosphorylation site and five potential glycosylation sites have been detected in the amino-acid sequence. Computer searches fail to reveal any significant homology with known proteins. Developmental pattern of transcription of the modulo gene indicates that messengers are maternally provided to the embryos and that zygotic transcription is required during subsequent development.