Retrons in Eubacteria and Archaea have reverse transciptase genes. Some are associated with Group II Introns. These prokaytoic retroelements are believed to have played an important role in prokaryotic evolution. It is unclear if they arose DeNovo in the prokayotes or if they were transfered by preLUCA world. Some mechanism must have been in place in the PreLuca world to transfer RNA genetic information into DNA form. It is believed that reverse transcpritase existed in the RNA world to perform this function. A RNA polymerase Ribozyme has been enginnered but a reverse transciptase has not yet to been identified. Nevetheless Group II Introns can slice into and out of DNA segments and ligate DNA segments. Therefore, It the evolution of the genetic code could be tied to the evolution of these types of ribozymes. The ability of mobile genetic elements to integrate into and out of mRNA, tRNA, and rRNA makes it tempting to speculate that the evolution of transcriptional and translational was orchestrated by retroid RNA..
Bacterial Group D Type II Introns
Chloroplast Type I Introns
Bacterial Retrons are involved in the production of msDNA and can be transfered by bacteriophages
II Retroid Transposable Elements
Retroid Viruses also contain contain genes for a capsid -GAG, reverse transcriptase, and integrase -POL. They can mobilize within the cell or occassionaly between cells
Present in nematodes and A deep-branching clade of retrovirus-like retrotransposons in bdelloid rotifers
Retroviruses contain genes for capsid, reverse transciptase, and envelope proteins . Their mobility is from cell to cell or multicellular organism to multicellular organism. Arthropod vectors have not been identified but it has been shown that trypanosomatids can host viruses that are subseqeuntly transfered by sand flys or other arthropod vectors. I hypothesize that dsDNA circle forms of HIV will be identified in Leishmania and determined to be a reservoir for recombinant new types.
3Ty/Gypsy Elements (prior to protostome-deuterostome divergence----->3 kings hypothesis for origin of of III Classes of Retroviruses----->Vertebartes--- >Fish ----->epsilon retroviruses---->Mammals and Avian Hosts ------> ( lentiviruses, alpharetroviruses, betaretroviruses, and deltaretroviruses)----->Rodents and Insectivores -----> betaretroviruses and Lentiviruses --->?trypansomatid vectors-----> RELIK/EIAV---->Carnivores-->ELIK/FIV---->proSIV---->SIV ------>HIV
V DNA retroviruses ie. Hepatitis B, and plant DNA retroviruses
ORF-less and reverse-transcriptase-encoding group II
introns in archaebacteria, with a pattern of homing
into related group II intron ORFs
Genome-wide detection of Ty1-copia and Ty3-gypsy
group retrotransposons in Japanese apricot (Prunus
mume Sieb. et Zucc.
Wochner A, Attwater J, Coulson A, Holliger P 2011 Ribozyme-Catalyzed Transcription of an Active Ribozyme Science 332 209-212