| Non-Scientific
Abstract Every time a eukaryotic cell¹s genome is replicated, some information is lost from
the extreme ends of each chromosome. These extreme ends are known as telomeres. Unchecked, this process could
result in the destruction of essential genes.Most organisms use an enzyme known as telomerase to add meaningless
DNA bases to the ends of chromosomes in order to counteract this information loss. Previous studies have shown
that the fruit fly, Drosophila melanogaster, while once a model organism for telomere studies, actually
uses a completely different system of telomere maintenance.Fruit fly chromosomes are extended through the action
of at least two families of retrotransposons,HeT-A and TART. These are segments of DNA which are capable of
placing copies of themselves elsewhere in a chromosome. In this case, they are copied to the telomeres. Our study
was designed to further the understanding of the evolution and mechanisms of action of TART. Particularly, we
studied the transcription and translation of TART DNA into protein. This included a searching of various segments
of TART for potential promoters, segments of DNA that are required for the transcription of a gene into RNA.We
also analyzed the RNA product of these segments to determine where in TART transcription began. Our results seem
to show the presence of a promoter in the upstream (or 5¹) end of the TART segment.We have also confirmed the
presence of an antisense promoter (a segment leading to upstream transcription) in the downstream (or 3¹) end of
TART.We now have an idea of where transcriptions begins, but further studies are required to confirm this.
Abstract Drosophila
melanogaster and some close relatives use two non-LTR retrotransposons,HeT-A and TART, to maintain their
telomeres rather than a telomerase. To understand the functional mechanisms and regulation of these elements, we
have begun to examine their promoters.HeT-A, unlike any other non-LTR retrotransposon, has been found to utilize
a 3¹ sense promoter. Due to the presence of sense and antisense TART transcripts and structural similarity to the
Dictyostelium Repetitive Element (DRE), it was hypothesized that TART had a promoter scheme similar to DRE. That
is, it has a sense promoter in the 5¹UTR which, even though its sequence is perfectly repeated in the 3¹UTR, does
not act as a promoter there.We also believed we would find an antisense promoter in the 3¹UTR. Segments of TART
DNA were isolated and cloned into a reporter plasmid to determine if they could act as promoters. Sense RNA
transcripts were recovered and analyzed to determine the location of the start of sense transcription, which
appears to occur approximately 1kb upstream of the end of the 5¹ UTR. |
