Analysis of CAG/CTG triplet repeats in the human genome: Implication in transcription factor gene regulation.
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Date
1995-12
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Abstract
Instability and polymorphism at several CAG/CTG trinucleotide repeat loci
have been associated with human genetic disorders. In an attempt to identify novel
sites that may be possible loci for expansion of CAG/CTG repeats, we searched all
human sequences in the EMBL nucleotide sequence database for (CAG)5 and (CTG)5
repeats. We have identified 121 human DNA sequences of known and unknown
functions that contain stretches of five or more CAG or CTG repeats. Many repeat
stretches were interrupted by variant triplets, a significant number of which differ
from the repeat triplet only by a single base, suggesting that these evolved from the
parent triplet by point mutations. A large number of human transcription factor genes
were found to contain CAG repeats within their coding sequences. Analysis of the
EMBL transcription factors database showed that many transcription factor genes of
other eukaryotes, including genes involved in Drosophila embryo development, possess
these repeats. Interestingly, CAG repeats are absent from prokaryotic transcription
factors. Different sequence entries for the human TATA box binding protein showed
a polymorphism in the length of the CAG repeat in this gene, suggesting that loci
other than those already known to be associated with genetic diseases may be possible
sites for repeat instability related disorders. On the basis of our findings in this
database analysis, we propose a role for CAG repeats as cis-acting regulatory elements
involved in fine-tuning gene expression.
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Keywords
Triplet repeats, sequence analysis, transcription factor genes, TBP
Citation
Bhandari Rashna, Bramachari Samir K. Analysis of CAG/CTG triplet repeats in the human genome: Implication in transcription factor gene regulation. Journal of Biosciences. 1995 Dec; 20(5): 613-627.