Isochore specificity of AUG initiator context of human genes.

The efficiency of AUG start codon recognition in translation initiation is modulated by its sequence context. Here we investigated a non-redundant set of 5914 human genes and show that this context is different in genes located in different isochores. In particular, of the two main consensus start sequences, RCCaugR is five-fold more represented than AARaugR in genes from the GC-rich H3 isochores compared to genes from the GC-poor L isochores. Furthermore, genes located in GC-rich isochores have shorter 5' UTRs and stronger avoidance of upstream AUG than genes located in GC-poor isochores. This suggests that genes requiring highly efficient translation are located in GC-rich isochores and genes requiring fine modulation of expression are located in GC-poor isochores. This is in agreement with independent data from the literature concerning the location of housekeeping and tissue-specific genes, respectively.