FEBS Lett., 390, 99-103 (1996)
The size differences among mammalian introns are
due to the accumulation of small deletions
Hiroyuki Ogata, Wataru Fujibuchi, Minoru Kanehisa*
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611, Japan
Abstract
In order to investigate the molecular mechanisms that alter the intron size, we conducted
an extensive interspecies comparison of homologous introns among three mammalian
groups: human, artiodactyls, and rodents. The size difference of introns was
statistically significant among all the three groups, and the intron was the longest for
human and the shortest for rodents. The intron size difference appears to be due to the
accumulation of small deletions, according to the separate count of insertion and
deletion frequencies. The distribution of intron size differences also has a shape similar
to the distribution of insertion/deletion sizes found in pseudogenes. It is suggested that
introns are selectively neutral to small-scale changes of the genome size, which
inherently contain the bias of favoring short deletions against short insertions.
Key words: Intron; Size difference; Deletion; Insertion; Mutation rate; Isochore family
*Corresponding author:
Minoru Kanehisa
Institute for Chemical Research, Kyoto University
Uji, Kyoto 611, Japan
Fax: +81-774-32-8235
E-mail: kanehisa@kuicr.kyoto-u.ac.jp