Influence of introns in protein evolution

Eukariotski geni sadrže egzone i introne. Egzoni sadrže informacije za sintezu polipeptidnog lanca, pa se zadržavaju u mRNA i ne izbacuju se iz primarnog transkripta. Introni ne sadrže informacije za sintezu polipeptida, pa se izbacuju iz primarnog transkripta procesom prekrajana. Eukarioti sadrže sve tipove introna, a najčešći su spliceosome-alni introne, uz koje su povezani fenomeni kojima se utjecalo na evoluciju proteina. Miješanje egzona omogućava stvaranje proteina s novom ili izmijenjenom funkcijom brže od dobivanja novih proteina mutacijama postojećih. Omogućavaju ga popravak dvolančanih lomova nehomolognom rekombinacijom i korelacija egzona sa strukturnim domenama proteina. Tako je dobivena većina eukariotskih proteina s ponavljajućim domenama. Alternativno prekrajanje olakšava postojanje višestaničnih organizama jer se štedi na prostoru koji zauzima genom: jednim genom omogućava se kodiranje različitih proteina čime se i pojačava efekt miješanja egzona. Prekrajanje egzona različitih primarnih transkripata naziva se trans-prekrajanje. Njime se još bolje može regulirati ekspresija gena i mogu se kombinirati različiti egzoni kako bi se pomoću prekrajanja odmah dobili proteini s novim funkcijama, a zastupljeno je i u genima organela. U prokariota intronski sustav je slabije zastupljen, pa je i utjecaj introna na proteine bio izražen samo tijekom evolucije tijekom horizontalnog prijenosa gena. Danas prokarioti imaju fenomen sličan alternativnom prekrajanju: shufflon.Eukaryotic genes contain exons and introns. Exons contain information for polypeptide chain synthesis, so they are retained in the mRNA and are not ejected from the primary transcript. Introns do not contain information for polypeptide synthesis, so they are ejected from the primary transcript by the spliceing process. Eukaryotes contain all types of introns, and the most common are spliceosomal introns, which are associated with phenomena that have influenced the evolution of proteins. Exon shuffling allows the creation of proteins with new or altered functions faster than obtaining new proteins by mutations of existing ones. It is enabled by the repair of double-stranded breaks by non-homologous recombination and the correlation of exons with the structural domains of proteins. Thus, most eukaryotic proteins with repeating domains were obtained. Alternative splicing facilitates the existence of multicellular organisms because it reduces space occupied by the genes: a single gene allows the encoding of different proteins, thus enhancing the effect of exon shuffling. Splicing the exons of different primary transcripts is called trans-splicing. It can even better regulate gene expression and combine different exons to instantly obtain proteins with new functions, and is also present in organelle genes. In prokaryotes, the intron system is less represented, so the influence of introns on proteins was expressed only during evolution by horizontal gene transfer. Today, prokaryotes have a phenomenon similar to the alternative splicing: shufflon