Putting the Brakes on Evolution

summary: to make proteins DNA > mRNA > aminoacid sequence which folds into a protein.
but in most human genes the mRNA must be modified by splicing out introns that aren't supposed to be tranlated into part of the protein. These scientists found that the DNA around the splicing sites mutates/evolves slower than genes that don't have introns.

pretty interesting, but introns have a function in creating proteins since the mRNA can be spliced in different ways (splicing exons together in different orders or leaving different exons out). For example the sex of fruit flies is determined by the alternative splicing of a gene.

As a biochemist learning the structure and function of proteins never ceases to amaze me. Evolution is incredible, even with these brakes.

Interesting. This is at PLoS too: Splicing and the Evolution of Proteins in Mammals, Evolutionary Influences on Proteins.

Most of the DNA in our genes is actually not involved in the specification of proteins. Rather, the bits with the protein-coding information (exons) are separated from each other by noncoding bits, introns. Before a gene can be translated into protein these introns are removed and the exons are spliced back together to be translated into protein. While information about which DNA to remove is largely in the introns themselves, parts of the exons near the intron–exon boundary can, for example, function as splice enhancer elements. In principle, then, these parts of exons have two functions: to specify the amino acids of the resulting protein and to enable the correct removal of introns. What impact might this have on a gene's evolution? We show that near intron–exon boundaries, amino acid usage is biased towards nucleotides involved in splice control. Moreover, these parts of genes evolve especially slowly. Indeed, we estimate that a gene with many exons would evolve at under half the rate of the same gene with no introns, simply owing to the need to specify where to remove introns. Likewise, genes that have lost their introns evolve especially fast near the former intron's location. Thus, human proteins may not be as optimised as they could be, as their sequence is serving two conflicting roles.

Perhaps the proportion of "Junk DNA" in us just shrunk.