Distribution profiles of GC content around the translation initiation site in different species.

We have analyzed the distribution of guanine-cytosine (GC) content around the translation initiation site in genomic DNA sequences of different species. A set of sequences belonging to one species is aligned at the translation initiation site, and the average GC content is calculated for 100 base windows over a range of 500 bases each for upstream and downstream region. Consistent with previous observations that coding regions are more GC-rich than non-coding regions, we observe a jump in the GC content at the translation initiation site, except for vertebrate sequences. It was also found that the overall shape of the GC content profile is similar within each organism group even though the average GC contents can be very different. Furthermore, by examining different profiles for different species, we have found a negative correlation between the average GC content and the jump size at the translation initiation site. Apparently, more AT-rich genomes, which tend to lack macroscopic mosaic structures, exhibit more marked differences in the GC content at the microscopic level.