Minimal introns are not "junk" - PubMed (original) (raw)

Minimal introns are not "junk"

Jun Yu et al. Genome Res. 2002 Aug.

Abstract

Intron-size distributions for most multicellular (and some unicellular) eukaryotes have a sharp peak at their "minimal intron" size. Across the human population, these minimal introns exhibit an abundance of insertion-deletion polymorphisms, the effect of which is to maintain their optimal size. We argue that minimal introns affect function by enhancing the rate at which mRNA is exported from the cell nucleus.

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Figures

Figure 1

Figure 1

Intron size for Homo sapiens (a), Arabidopis thaliana (b), Drosophila melanogaster (c), and Caenorhabditis elegans (d). There is always a species-specific minimum intron size, at which a significant fraction of the introns tend to cluster. This “spike” in the distribution is centered around the mean (±SD) intron sizes of 92±14, 89±12, 61±10, and 48±9 bp, respectively. For larger introns, the size distribution is highly species-specific. In the extreme case, H. sapiens, there is a broad “hump” attributable to transposon insertions inside the introns. Color indicates GC content: Red is GC-rich; blue, AT-rich.

Figure 2

Figure 2

Resequenced introns, shown against the joint distribution for intron size and GC content. Introns with a detectible transposon are colored blue; introns with no detectible transposons, gray. The 93 introns that we resequenced are red. They are selected to sample the full range of GC contents, and their mean size is 94±14 bp.

Figure 3

Figure 3

Insertion-deletion (indel) direction, relative to the major allele, as a function of intron size. For the 10 rare indels of minor allele frequency f < 0.06 (blue), the resultant size changes drive the introns back to their optimal size of 92 bp. The two common indels with f > 0.35 (red) are the only exceptions to this rule, presumably because they arose from a different population dynamics.

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