Summary: Determinants of Adaptive Evolution at the Molecular Level: the Extended
Bioinformatics Research Center, North Carolina State University, Raleigh
To explain why informational genes (i.e., those involved in transcription, translation, and related processes) are less
likely than housekeeping genes to be horizontally transferred, Jain and coworkers proposed the complexity hypothesis.
The underlying idea is that informational genes belong to large, complex systems of coevolving genes. Consequently, the
likelihood of the successful horizontal transfer of a single gene from such an integrated system is expected to be low.
Here, this hypothesis is extended to explain some of the determinants of the mode of evolution of coding sequences. It is
proposed that genes belonging to complex systems are relatively less likely to be under adaptive evolution. To evaluate
this ``extended complexity hypothesis,'' 2,428 families and protein domains were analyzed. This analysis found that
genes whose products are highly connected, located in intracellular components, and involved in complex processes and
functions were more conserved and less likely to be under adaptive evolution than are other gene products. The extended
complexity hypothesis suggests that both the mode and the rate of evolution of a protein are influenced by its gene
ontology (localization, biological process, and molecular function) and by its connectivity.
Finding the determinants of a protein's rate of
evolution has proved a difficult task, but recent evidence
from the yeast Saccharomyces cerevisiae suggests that the
rate of evolution of a protein correlates positively with