H0W D0 TETR0TRANSP0S0NS W0RKRetr0transp0s0n; – Retr0transp0s0ns als0 called transp0s0ns via RNA intermediate are genetic, elements that can amplify themselves in a gen0me and are ubiquit0us c0mp0nents 0f the, DNA 0f many eukary0tic 0rganisms. These DNA sequences use a “c0py-and-paste” mechanism, whereby they are first, transcribed int0 RNA, then c0nverted back int0 identical DNA sequences using reverse, transcripti0n, and these sequences are then inserted int0 the gen0me at target site. Retr0transp0s0ns f0rm 0ne 0f the tw0 subclasses 0f transp0s0ns, where 0thers, are, DNA transp0s0ns, which d0 n0t inv0lve an RNA intermediate. Retr0transp0s0ns are particularly abundant in plants, where they are 0ften to main, c0mp0nent 0f nuclear DNA.
In maize, 49-78% 0f the gen0me is made up 0f, retr0transp0s0ns.In wheat, ab0ut 90% 0f the gen0me c0nsists 0f repeated sequences and 68% 0f, transp0sable elements.In mammals, alm0st half the gen0me (45% t0 48%) is transp0s0ns 0r remnants 0f, transp0s0ns.
Ar0und 42% 0f the human gen0me is made up 0f retr0transp0s0ns, while DNA, transp0s0ns acc0unt f0r ab0ut 2-3%.Bi0l0gical activity; – Retr0transp0s0ns’ replicative m0de 0f transp0siti0n by means 0f an RNA, intermediate rapidly increases the c0py Bi0l0gical activity numbers 0f elements and, thus can increase gen0me size. Like DNA transp0sable elements (class II transp0s0ns), retr0transp0s0ns can be induced by inserting near 0r genes. Furtherm0re, retr0transp0s0n-induced mutati0ns are relatively stable, because the sequence at the insertion site is retained as they transp0se via the replicati0n mechanism. Retr0transp0s0ns c0py themselves t0 RNA and then back t0 DNA that may, integrate back t0 the gen0me. Sec0nd step 0f f0rming DNA may be carried out by a, reverse transcriptase, which the retr0transp0s0n enc0des. Transp0siti0n and survival 0f, retr0transp0s0ns within the h0st gen0me are p0ssibly regulated b0th by retr0transp0s0n-, and h0stenc0ded fact0rs, t0 av0id deleteri0us effects 0n h0st and retr0transp0s0n as well.
Understanding 0f h0w retr0transp0s0ns and their h0sts’ gen0mes have c0-ev0lved, mechanisms t0 regulate transp0siti0n, inserti0n specificities, and mutati0nal 0utc0mes in, 0rder t0 0ptimize each 0ther’s survival is still in its infancy. Because 0f accumulated mutati0ns, m0st retr0transp0s0ns are n0 l0nger able t0, retr0transp0se.Types; -Retr0transp0s0ns, als0 kn0wn as class I transp0sable elements. It has tw0 types;LTR (L0ng Term Repeat) retr0transp0s0ns,N0n-LTR retr0transp0s0ns, The above classificati0n is based 0n the phyl0geny 0f the reverse transcriptase, which, g0es in line with structural differences, such as presence / absence 0f l0ng terminal, repeats as well as number and types 0f 0pen reading frames, enc0ding d0mains and, target site duplicati0n lengths.
LTR retr0transp0s0ns; – LTR retr0transp0s0ns have direct LTRs that range fr0m ~ 100 bp t0 0ver 5 kb in size. LTR retr0transp0s0ns are further sub-classified int0;Ty1-c0pia-like (Pseud0viridae),Ty3-gypsy-like (Metaviridae),BEL-Pa0-like gr0ups, These are 0n b0th their degree 0f sequence similarity and 0rder 0f, enc0ded gene pr0ducts.Ty1-c0pia and Ty3-gypsy gr0ups 0f retr0transp0s0ns are c0mm0nly f0und in high c0py, number (up t0 a few milli0n c0pies per hapl0id nucleus) in animals, fungi, pr0tista, and, plants gen0mes.BEL- Pa0 like elements has been far 0nly been f0und in animals. Alth0ugh retr0viruses are 0ften classified separately; they share many features with, LTR retr0transp0s0ns.
A maj0r difference with Ty1-c0pia and Ty3-gypsy retr0transp0s0ns, is that retr0viruses have an envel0pe pr0tein (ENV). A retr0virus can be transf0rmed int0, an LTR retr0transp0s0n thr0ugh inactivati0n 0r deleti0n 0f the d0mains that enable, extracellular m0bility. If such a retr0virus infects and subsequently inserts itself in the, gen0me in germ line cells, it may be transmitted vertically and bec0me an, End0gen0us Retr0virus (ERV). End0gen0us retr0viruses make up ab0ut 8% 0f the, human gen0me and appr0ximately 10% 0f the m0use gen0me.
In plant gen0mes, LTR, retr0transp0s0ns are the repetitive sequence class, e.g. able t0 c0nstitute m0re, than 75% 0f the maize gen0me.End0gen0us retr0viruses (ERV); – End0gen0us retr0viruses are the m0st imp0rtant LTR retr0transp0s0ns in mammals, including humans where the Human ERVs make up 8% 0f the gen0me.