The effect of the transcriptional activator GAGA factor on position effects at the rolled locus in Drosophila melanogaster



Gonsalves, Allison Jardim

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University of Guelph


In 'Drosophila', heterochromatin, the region of the chromosome that remains condensed through most of the cell cycle, is known to house a few vital, mutable genes. One of these genes, the 'rolled' locus is normally located deep in the heterochromatin of the right arm of the second chromosome. The function of the 'rl' gene can be severely affected in rearrangements that translocate 'rl', in a small block of associated heterochromatin, to distal euchromatic regions. These position effects can be reverted, and have been shown to result in a significant decrease of mRNA transcription and a visible 'rolled' phenotype. The main focus of this thesis was to examine the effects that an enhancer of euchromatic position effects and transcriptional activator, GAGA factor (GAF), has on the position effects at the 'rolled' locus. Hypomorphic alleles of 'Trithorax-like', the gene encoding GAF were introduced into the 'rl'+ rearrangement strains. This experiment shows that the hypomorphic alleles of 'Trl ' ('Trl62, Trl13C' and ' TrlR85') act as suppressors of 'rolled' position effect in the 'T'('2;3') '76-7, T'('2;3')'127-1', 'T'(' 2;3')'127-3' and 'T'('2;3')' 127-4' strains. Immunofluorescent localization on polytene chromosomes indicates that GAF is largely excluded from the heterochromatic chromocentre in the nuclei of all strains examined. RNA analysis of two of the rearrangement strains in a 'Trl' or + background indicate that the suppression of 'rolled' position effect occurs at the level of transcription. This result implicates GAF in the regulation of expression of the ' rolled' gene. Thus, this thesis demonstrates that a protein that enhances euchromatic gene position effect variegation suppresses position effects associated with a heterochromatic gene. These results clearly imply a functional differentiation between euchromatic and heterochromatic genes.



Drosophila melanogaster, heterochromatin, rolled locus gene, euchromatic position effects, transcriptional activator, GAGA factor, position effects