Synonymous and nonsynonymous substitutions in mammalian genes: intragenic correlations

Previous investigations indicated that synonymous and nonsynonymous substitution rates are correlated in mammalian genes. In the present work, this correlation has been studied at the intragenic level using a dataset of 48 orthologous genes from species belonging to at least four different mammalian orders. The results obtained show that the intragenic variability in synonymous rates is correlated with that of nonsynonymous rates. Moreover, the variation in GC level (and especially of C level) of silent positions along each gene is correlated with the variation in synonymous rate. These results reinforce the previous conclusions that synonymous and nonsynonymous rates as well as GC levels of silent positions are to some extent under common selective constraints.