Molecular genetic analysis of the Drosophila melanogaster Trithorax-like gene coding for the GAGA transcription factor

The Drosophila melanogaster Trithorax like (Trl) gene is classed with the t rx-G genes and codes for several isoforms of the GAGA transcription factor (GAF) which regulates expression of homeotic and numerous other genes. GAF acts as a transcriptional antirepressor, i.e., its interaction with nucleos omal DNA results in the open chromatin conformation in promoter gone region s. The regions thereby become accessible to other transcription factors. As mutations of the Trl gene enhance position effect variegation and disturb chromosome segregation in mitosis and meiosis, GAF is thought to play anoth er, more significant role in determining the chromatin structure. To study the molecular basis of its pleiotropic effect, the Trl gene was subjected t o a structural analysis. The genomic fragment encompassing Trl gene was seq uenced, the sizes of its exons and introns was established, and a complex s tructure of the 5' and 3' gene regions was demonstrated. The Trl(13C), Trl( 62), DfTrl(R67), and DfTrl(R85) mutations were exactly mapped. In addition, four insertions of the P element were identified as Trl alleles (Trl(l(3)s 2325), Trl(EP(3)3184), Trl(EP(3)3191), and Trl(EP(3)3609)). The viability a t various developmental stages was studied in homozygotes for the Trl mutat ions and in interallelic compounds. The following lethality stages were est ablished: hatching, (Trl(13C), DfTrl(R85), Trl(EP(3)3609)), larval molts (T rl(l(3)s2325)), pupation, metamorphosis (DfTrl(R67), Trl(62)), and eclosion (some compounds).