Origin of the human L1 elements: proposed progenitor genes deduced from a consensus DNA sequence

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• Long interspersed repeated DNA elements (LINEs) are abundant in eukaryotic genomes.
• The human L1Hs (LINE or KpnI sequence) element is a major component of the human genome.
• Understanding L1Hs structure and evolution is crucial for deciphering genome dynamics.

Purpose of the Study:

• To present a consensus sequence for the human L1Hs element.
• To analyze the structure, homology, and potential function of L1Hs open reading frames (ORFs).
• To investigate the evolutionary history and origin of human L1 sequences.

Main Methods:

• Sequence analysis to derive a consensus L1Hs sequence.
• Homology searches to compare L1Hs ORFs with known sequences.
• Phylogenetic analysis to infer evolutionary relationships and estimate element age.
• Comparative genomics to assess species-specificity.

Main Results:

• The L1Hs consensus sequence features two ORFs with homology to other species' L1 elements.
• The 5' end contains terminators and homology to Alu repeats; the 3' ORF predicts a 149 kD protein with reverse transcriptase-like domains.
• Most L1 elements are likely untranslatable due to sequence variations, suggesting derivation from a limited set of genes.
• Human L1 sequences show species-specificity compared to other mammals, with most generated within the last 30 million years.

Conclusions:

• The L1Hs consensus sequence provides a reference for studying these mobile elements.
• L1 elements likely evolved through mechanisms like retroposition and transposition.
• The observed species-specificity and estimated age shed light on the recent expansion of L1 in the human genome.