The helix-loop-helix proteins dAP-4 and daughterless bind both in vitro and in vivo to SEBP3 sites required for transcriptional activation of the Drosophila gene Sgs-4.
The expression of Sgs genes in the salivary gland of the third instar larva of Drosophila is a spatially restricted response to signalling by the steroid hormone 20-hydroxyecdysone. For Sgs-4, we have previously demonstrated that its strictly tissue and stage-specific expression is the result of combined action of the ecdysone receptor and secretion enhancer binding proteins (SEBPs). One of these SEBPs, SEBP2, was shown to be the product of the homeotic gene fork head. Together with SEBP3, SEBP2 appears to be responsible for the spatial restriction of the hormone response of Sgs-4. Here, we show that SEBP3 is a heterogeneous binding activity that consists of different helix-loop-helix (HLH) proteins. We cloned the Drosophila homologue of human transcription factor AP-4 (dAP-4) and identified it as one of these HLH proteins. The dAP-4 protein shows great similarity to its human and Caenorhabditis counterparts within the bHLHZip domain, the second leucine zipper dimerization motif, and a third region of unknown function. The expression pattern of dAP-4 indicates that it is a ubiquitously expressed HLH protein in Drosophila. As a second component of SEBP3 we identified the Daughterless (Da) protein, which is also ubiquitously expressed and binds to SEBP3 sites independent of dAP-4. Since both dAP-4 and Da can be detected in situ at transposed Sgs-4 transcriptional control elements in polytene salivary gland chromosomes, we propose that each of the two proteins contributes to the transcriptional control of Sgs-4.
King-Jones
K
K
Institut für Genetik der Freien Universität Berlin, Arnimallee 7, Berlin, D-14195, Germany.
Korge
G
G
Lehmann
M
M
D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001665:Binding Sites; D004251:DNA Transposable Elements / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation; D005967:Glue Proteins, Drosophila / Q000235:genetics*; D018257:Helix-Loop-Helix Motifs; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D019476:Insect Proteins / Q000378:metabolism; D008840:Microfilament Proteins; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D012045:Regulatory Sequences, Nucleic Acid; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation
D051792:Basic Helix-Loop-Helix Proteins; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D051858:Forkhead Transcription Factors; D005967:Glue Proteins, Drosophila; D018398:Homeodomain Proteins; D019476:Insect Proteins; D008840:Microfilament Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; C090080:Da protein, Drosophila; C055473:enhancer-binding protein AP-4; C084628:f protein, Drosophila; C512745:fkh protein, Drosophila