Natural Transposon: Dmel\HeT-A
Natural Transposon: Dmel\HeT-A
3 in euchromatin of Release 3 genome annotation, of which zero are full length.
HeT-A and TART-element, previously considered to be closely related, have very different transcriptional characteristics. Additionally, features of TART-element sequence organisation resemble those of a subclass of non-LTR elements characterized by unequal terminal repeats. The distinctive transcription patterns of HeT-A and TART-element are conserved in D.yakuba.
HeT-A sequences have been found in the centric heterochromatin of chromosome 3.
The HeT-A promoter is at the 3' end of the element and directs transcription of the HeT-A element immediately downstream in the tandem array in which they are found. The HeT-A element appears to be an evolutionary intermediate between LTR and non-LTR retrotransposons. Considering two HeT-A elements in tandem array, the promoter-containing 3' end of the upstream element is identical to the promoter-containing 3' end of the downstream element, and this "extended element" is structurally and functionally equivalent to an LTR retrotransposon. The promoter-containing 3' end of the upstream element acts as a surrogate for the 5' LTR characteristic of the LTR retrotransposon, although it is actually part of the flanking element. The HeT-A element does not encode its own reverse transcriptase.
Comparison of integrase/transposase domains to new elements containing the DDE signature.
HeT-A promoter activity is located in the 3' end of the element. In HeT-A arrays the 3' sequence of one element directs transcription of its downstream neighbour.
HeT-A retrotransposons hybridise close to the centromere of the Y chromosome.
HeT-A element and TART-element may be evolutionarily related to telomerase, in both cases an enzyme extends the end of a chromosome by adding DNA copied from an RNA template.
A HeT-A element has been cloned and sequenced. The unit length of the HeT-A element is approximately 6kb.
The HeT-A element is approximately 6kb in length. It can be divided into three regions; a protein coding region composed of two overlapping reading frames, a 5' non-coding region and a 3' non-coding region (which makes up approximately half the HeT-A element).
Analysis of HeT-A transcripts suggests that HeT-A elements transposase by means of a polyadenylated RNA intermediate and that each element joins to the chromosome end by means of the poly(A) tail of the RNA.
The genomic organization (oligo(A) tails facing proximally at chromosome ends) and sequence analysis of 29 different HeT-A fragments supports the model of telomere elongation by transposition of HeT-A elements.
HeT-A sequences are never found in the euchromatin. Y associated HeT-A clusters have significantly different structures than telomeric clusters, and may arise by different transposition mechanisms.
A transposon family of non-long terminal repeat retrotransposons found at the telomere. HeT-A elements transpose to broken chromosome ends. Evidence suggests that they can also transpose to natural chromosome ends.
Transposition of HeT-A onto broken chromosome ends is implicated in chromosome healing. Ends of X chromosomes with new HeT-A additions receded at the same rate as broken ends before HeT-A elements attached. Approximately 1% of chromosomes per generation aquired new HeT-A sequences of an average of 6kb at their ends, and the rate of addition of new material per generation matches the observed rate of loss caused by incomplete replication at the ends of the DNA molecule. Transposition of HeT-A onto broken chromosome ends is implicated in chromosome healing. Ends of X chromosomes with new HeT-A additions receded at the same rate as broken ends before HeT-A elements attached. Approximately 1% of chromosomes per generation aquired new HeT-A sequences of an average of 6kb at their ends, and the rate of addition of new material per generation matches the observed rate of loss caused by incomplete replication at the ends of the DNA molecule.
HeT-A is a transposable element that heals broken chromosomes: it may have a structural role in telomere organization or maintenance.
HeT-As is transcribed and are conserved in the D.melanogaster species subgroup. It may play a role in the structure and/or function of telomeres.
Sequence of a HeT-A element includes two overlapping open reading frames that are one nucleotide out of frame with respect to each other. The longer ORF contains Cys-His motifs strongly resembling nucleic acid binding domains of gag-like proteins and the overall organisation is reminiscent of LINE elements.
construct_comment: Associated with telomeres.
The distribution of different subfragments of HeT-A DNA throughout the genome has been studied.
HeT-A may have a role in organizing or maintaining the ends of chromosomes. The association of HeT-A with the newly acquired telomeres, in a formerly euchromatic region of C(1)A, strengthens this correlation.