LINEs[edit source |
editbeta]
Long INterspersed Elements[9] are a group of genetic elements that are found in large numbers
in eukaryotic genomes. They are transcribed to an RNA using an RNA polymerase II
promoter that resides inside the LINE. LINEs code for the enzyme reverse transcriptase,
and many LINEs also code for an endonuclease (e.g.
RNase H). The
reverse transcriptase has a higher specificity for the LINE RNA than other RNA,
and makes a DNA copy of the RNA that can be integrated into the genome at a new
site.[10] The
endonuclease encoded by non-LTR retroposons may be AP (Apurinic/Pyrimidinic)
type or REL (Restriction Endonuclease Like) type. R2 group of elements have REL
type endonuclease which shows site specificity in insertion.[11]
The 5' UTR contains the
promoter sequence, while the 3' UTR contains a polyadenylation signal (AATAAA)
and a poly-A
tail.[12] Because
LINEs (and other class I transposons, eg. LTR retrotransposons and SINEs) move
by copying themselves (instead of moving by a cut and paste like mechanism, as
class II transposons do),
they enlarge the genome. The human genome, for example, contains about 500,000
LINEs, which is roughly 17% of the genome.[13] Of
these, approximately 7,000 are full-length, a small subset of which are capable
of retrotransposition.[14][15]
Interestingly, it was recently found that specific LINE-1
retroposons in the human genome are actively transcribed and the associated
LINE-1 RNAs are tightly bound to nucleosomes and essential in the establishment
of local chromatin
environment.[16]
Activation of Human Long
Interspersed Nuclear Element 1 Retrotransposition by Benzo(a)pyrene, an
Ubiquitous Environmental Carcinogen
Kenneth S. Ramos, Department of Biochemistry and Molecular Biology, University
of Louisville, Louisville, KY
editbeta]
Long INterspersed Elements[9] are a group of genetic elements that are found in large numbers
in eukaryotic genomes. They are transcribed to an RNA using an RNA polymerase II
promoter that resides inside the LINE. LINEs code for the enzyme reverse transcriptase,
and many LINEs also code for an endonuclease (e.g.
RNase H). The
reverse transcriptase has a higher specificity for the LINE RNA than other RNA,
and makes a DNA copy of the RNA that can be integrated into the genome at a new
site.[10] The
endonuclease encoded by non-LTR retroposons may be AP (Apurinic/Pyrimidinic)
type or REL (Restriction Endonuclease Like) type. R2 group of elements have REL
type endonuclease which shows site specificity in insertion.[11]
The 5' UTR contains the
promoter sequence, while the 3' UTR contains a polyadenylation signal (AATAAA)
and a poly-A
tail.[12] Because
LINEs (and other class I transposons, eg. LTR retrotransposons and SINEs) move
by copying themselves (instead of moving by a cut and paste like mechanism, as
class II transposons do),
they enlarge the genome. The human genome, for example, contains about 500,000
LINEs, which is roughly 17% of the genome.[13] Of
these, approximately 7,000 are full-length, a small subset of which are capable
of retrotransposition.[14][15]
Interestingly, it was recently found that specific LINE-1
retroposons in the human genome are actively transcribed and the associated
LINE-1 RNAs are tightly bound to nucleosomes and essential in the establishment
of local chromatin
environment.[16]
Activation of Human Long
Interspersed Nuclear Element 1 Retrotransposition by Benzo(a)pyrene, an
Ubiquitous Environmental Carcinogen
Kenneth S. Ramos, Department of Biochemistry and Molecular Biology, University
of Louisville, Louisville, KY