Terminal Redundancy (Molecular Biology)

Terminal redundancy is the existence of similar base-pair sequences at both ends of a linear DNA molecule. This is a common feature of many retroviral genomes. Many retroviruses and retrotransposons in the eukaryotic genome have identical or almost identical long terminal repeats (LTRs) at their ends. The length of the LTR is usually between 250 and 600 bp. There is less sequence conservation between the LTRs than within the body of the retrovirus or retrotransposon. The conserved sequences in the LTR required for retrotransposon function are the promoter sequences, sites of transcription and poly A addition, and short inverted repeats at the ends of each LTR. The activity of promoter sequences in LTRs is a potential source of genomic instability and inappropriate transcription within the chromosome (1). It has been proposed that a major function of the methylation of CpG sequences in vertebrates is to silence such transcriptional activity and to prevent transposition events. It is sometimes difficult to discriminate between bona fide promoters in chromosomal DNA and the evolutionary relics of LTRs (2).