We analysed Total-Genomic and EST
sequences for imperfection in di-, tri-, tetra- and pentanucleotide repeats
longer than 10 bases. The important observations we made in our data are
- Interruption of the perfect
the means of mutations is predominantly seen in the center of the repeat track.
- Mutations at 3′ end of the repeat
motif are few but not uncommon, whereas, 5′ mutations are rarely found although
they do exist.
- Shortest imperfect
repeats were identified in di-, tri- and tetranucleotide repeats of
15 bases in length.
- The longest imperfect repeat was a
tetranucleotide repeat of 611 bases.
(29/74) was found to be abundant in EST sequences compared to other
type of mutations, whereas insertion was least
accounted for 74% of the interruptions of perfect repeats, whereas insertion/deletions were observed in
only 26% of the interruptions in ESTS.
to Adenine was the most common mutations disrupting repeat continuity in
- In total-Genomic sequences, repeats were interrupted
most often by deletions (153/417), and least
by insertions (19/417).
- Ratio of transition/transversion to insertion/deletion
was found to be around 3:2 in total-Genomic sequences.
Adenine to Guanine and Thymine to Adenine
were the most common mutation disrupting the repeat continuity in total-Genomic
- Double mutations, in which two types
of mutations co-exist, were observed in 53 repeats (4 in ESTs and 49 in Genomic).
Among these, double transitions and double transversions occured together in 10
and repeat motifs respectively; transition and transversions were associated together
in 11/53: indels were together in 4/53; and indels and substitutions were associated
in 23/53 imperfect repeats.
- Triple mutations occurred together in 9 repeat motifs while one (AC)n
motif showed all the possible four mutations.