Ds. Dwyer, ASSEMBLY OF EXONS FROM UNITARY TRANSPOSABLE GENETIC ELEMENTS - IMPLICATIONS FOR THE EVOLUTION OF PROTEIN-PROTEIN INTERACTIONS, Journal of theoretical biology, 194(1), 1998, pp. 11-27
The discovery of ''genes-in-pieces'' provided the first evidence that
modern proteins evolved through the assembly and shuffling of simpler
building blocks-generally equated with exons. In the theoretical model
presented here, it is suggested that exons were created from even sma
ller modules that have been termed duplication units. Furthermore, the
se segments may represent the ultimate building blocks for protein ass
embly. The nucleotide sequences of the duplication units appear to res
emble those of mobile genetic elements such as transposons or insertio
n sequences, i.e. they possess direct repeats at each end and inverted
sequences extending 15-25 base pairs from these direct repeats. Durin
g evolution, these transposable exons (trexons) would have been replic
ated and dispersed in the genome thereby promoting homologous recombin
ation and further duplication. Thus, the transposition and splicing of
these gene segments gave rise to increasingly complex proteins as wel
l as multi-gene families of proteins. It has been proposed that peptid
es encoded by the first trexons were predisposed to form dimers or oli
gomers. Detailed structural analysis of various protein-protein comple
xes has revealed a tendency for the duplication units to self-associat
e. Self-binding peptides could have ultimately led to the evolution of
protein ligands and receptors with high affinity. (C) 1998 Academic P
ress.