LINEs:

LINEs (long interspersed nuclear elements) are a non-LTR Retrotransposons, a type of genome-wide repeat, often with transposable activity.

In eukaryotes, these repetitive elements constitute a large portion of its genome. There are about 850,000 repetitions of these, constituting about 21% of human DNA.

Repetitive sequences of the genome are classified into sub-divisions based on their size and the SINEs (short interspersed elements), with a length between 100 and 300 pair of bases , and LINEs are the major classes of repeats.

LINEs have a length between 4-6 kb and many sequences, smaller, whit about 1kb, derive them.  They’re replicated and propagated genome’s components which propagate in genome by auto replication, moving to new locations of DNA by a process called transposition.

These sequences represent reverse-transcribed RNA molecules originally transcribed by RNA polymerase II into mRNA and code for 2 proteins.

A typical LINE (fig 1) contains a 2 ORFs (open reading frames), a 3′ UTR (untranslated region), and 5′ UTR that contains an internal polymerase II promoter sequence, while the 3′ UTR contains a polyadenylation signal (AATAAA) and a poly-A tail.

LINE -1 is an example of a human LINE.

Their function in cell is not known, such as SINEs.

Fig 1-The components of a typical LINE. (5′ UTR, 2 ORFs and  3′ UTR with a polyadenylation signal (AATAAA) ).