Leader Sequence

The region of a messenger RNA (mRNA) molecule that precedes the coding sequence of a gene is called the ‘leader sequence’. This region is also known as the ‘five prime untranslated region’ (Figure 1) of the mRNA. Leader sequences have the propensity for forming secondary structures (stem-loops) by base pairing of complementary sequences. They are involved in the regulation of gene expression in eukaryotes and prokaryotes. In eukaryotes, the leader sequence may vary from few nucleotides to more than 1000 nucleotides. In prokaryotes, the leader sequences are usually short and at times contain an attenuator segment that is translated to a short-leader peptide. The leader peptide functions to terminate transcripts before the RNA polymerase reaches the first structural gene of the operon. The leader sequences in viruses have been shown to play an important role in the regulation of gene expression, replication, and pathogenicity. Mutations in the leader sequences of cellular mRNAs can have implications for disease and tumorigenesis.