Link Between Short tandem Repeats and Translation Initiation Site Selection.

Recent work in yeast and humans suggest that evolutionary divergence in cis-regulatory sequences impact translation initiation sites (TISs). Cis-elements can also affect the efficacy and amount of protein synthesis. Despite their vast biological implication, the landscape and relevance of short tandem repeats (STRs)/microsatellites to the human protein-coding gene TISs remain largely unknown. Here we characterized the STR distribution at the 120 bp cDNA sequence upstream of all annotated human protein-coding gene TISs based on the Ensembl database. Furthermore, we performed a comparative genomics study of all annotated orthologous TIS-flanking sequences across 47 vertebrate species (755,956 transcripts), aimed at identifying human-specific STRs in this interval. We also hypothesized that STRs may be used as genetic codes for the initiation of translation. The initial five amino acid sequences (excluding the initial methionine) that were flanked by STRs in human were BLASTed against the initial orthologous five amino acids in other vertebrate species (2,025,817 pair-wise TIS comparisons) in order to compare the number of events in which human-specific and non-specific STRs occurred with homologous and non-homologous TISs (i.e. [≥]50% and <50% similarity of the five amino acids). We characterized human-specific STRs and a bias of this compartment in comparison to the overall (human-specific and non-specific) distribution of STRs (Mann Whitney p=1.4 x 10-11). We also found significant enrichment of non-homologous TISs flanked by human-specific STRs (p<0.00001). In conclusion, our data indicate a link between STRs and TIS selection, which is supported by differential evolution of the human-specific STRs in the TIS upstream flanking sequence.\n\nAbbreviations