J. Brosius *
Institute of Experimental Pathology/Molecular Neurobiology, ZMBE, University of Muenster, Von-Esmarch-Str. 56, D-48149 Muenster, Germany
* Tel.: +49-251-835-8511. fax:
+49-251-835-8512.
E-mail: rna.world@uni-muenster.de
While the significance of middle repetitive elements had been neglected
for a long time, there are again tendencies to ascribe most members of
a given middle repetitive sequence family a functional role — as if the
discussion of SINE (short interspersed repetitive elements) function only
can occupy extreme positions. In this article, I argue that differences
between the various classes of retrosequences concern mainly their copy
numbers. Consequently, the function of SINEs should be viewed as pragmatic
such as, for example, mRNA-derived retrosequences, without underestimating
the impact of retroposition for generation of novel protein coding genes
or parts thereof (exon shuffling by retroposition) and in particular of
SINEs (and retroelements) in modulating genes and their expression. Rapid
genomic change by accumulating retrosequences may even facilitate speciation
[ McDonald, J.F., 1995. Transposable elements: possible catalysts of organismic
evolution. Trends Ecol. Evol. 10, 123–126.] In addition to providing mobile
regulatory
elements, small RNA-derived retrosequences including SINEs can,
in analogy to mRNA-derived retrosequences, also give rise to novel small
RNA genes. Perhaps not representative for all SINE/master gene relationships,
we gained significant knowledge by studying the small neuronal non-messenger
RNAs, namely BC1 RNA in rodents and BC200 RNA in primates. BC1 is the first
identified master gene generating a subclass of ID repetitive elements,
and BC200 is the only known Alu element (monomeric) that was exapted as
a novel small RNA encoding gene. Tables:
http://www-ifi.uni-muenster.de/exapted-retrogenes/tables.html
Additional References:
1. Frenster JH, "Nuclear RNA Species Activate DNA Transcription within Chromatin".
2. Gottesfeld JM, and Barbas CF III, "RNA as a Transcriptional Activator".
3. Hovsepian JA, and Frenster JH, "RNA-Induced Melting of DNA during Selective Gene Transcription".
4. Saha S, Ansari AZ, Jarell KA, and Ptashne M, "RNA Sequences that Work as Transcriptional Activating Regions".
5. Frenster JH, "Ultrastructural Probes of Active
DNA Sites, and the RNA Activators of DNA".