Relationship Between the Total Size of Exons and Introns
in Protein-coding Genes of Higher Eukaryotes
Hiroto Naora and Nicholas J. Deacon
Proceedings of National Academy of Sciences, 79:6196-6200 (1982)
Abstract
We have attempted to ascertain the correlation between the genetic
information content in the exons and the surrounding intron sequences
with regard to their spatial arrangement within a gene. A comparison
is made of the sizes, taken from recent publications, of exons and
introns of ~80 different protein-coding chromosomal genes, mostly from
higher eukaryotes. The exons of these genes do not show very marked
variation in size and can be classified into three major discrete
and two additional size groups, whereas individual introns vary
considerably in size within and between genes. Notwithstanding, the
overall length of all introns present within a given gene is a function
of the total size, mostly corresponding to the total genetic information
content, of the exons. Three cases that violate this exon-size
dependency of introns are genes coding for (i) histone H1, feather
keratin, and interferons, (ii) tubulin and actin, and (iii) silk
fibroin. The exons of these genes are larger than 0.7 kilobase pair
in total size and the genes show a strong sequence homogeneity
among the repetitious family members or internal repeats of coding
sequences within the gene. We propose that conservation of sequences,
which is required by the family members, internal repeats, or the entire
gene, would actually motive the removal of introns.
