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Postoje također i male interferne RNK (siRNK, 20-25&nbsp;nt) koje često nastaju razgradnjom RNK virusa, a postoje i endogeni izvori siRNK<ref>{{cite journal|author=Vazquez F, Vaucheret H, Rajagopalan R, ''et al.''|title=Endogenous ''trans''-acting siRNAs regulate the accumulation of ''Arabidopsis'' mRNAs|journal=Molecular Cell|year=2004|volume=16|issue=1|pages=69-79}}</ref><ref>{{cite journal|author=Watanabe T, Totoki Y, Toyoda A, ''et al.''|title=Endogenous siRNAs from naturally formed dsRNAs regulate transcripts in mouse oocytes|journal=Nature|volume=453|issue=7194|pages=539-43|year=2008|month=maj}}</ref>. siRNK mogu djelovati i preko RNK interference slično kao i kod miRNK. Neke miRNK i siRNK mogu na određenim ciljnim genima prouzrokovati metiliranje, te tako usporiti ili ubrzati transkripciju tih gena<ref>{{cite journal|author=Sontheimer EJ, Carthew RW|title=Silence from within: endogenous siRNAs and miRNAs|journal=Cell|volume=122|issue=1|pages=9-12|year=2005|month=juli}}</ref><ref>{{cite journal|author=Doran G|title=RNAi - Is one suffix sufficient?|journal=Journal of RNAi and Gene Silencing|year=2007|volume=3|issue=1|pages=217-19|url=http://libpubmedia.co.uk/RNAiJ-Issues/Issue-5/Doran.htm}}</ref><ref>{{cite journal|author=Pushparaj PN, Aarthi JJ, ''et al.''|title=RNAi and RNAa - The Yin and Yang of RNAome|journal=Bioinformation|volume=2|issue=6|pages=235-7|year=2008}}</ref>. Životinjske ćelije imaju piwi-interakcionu RNK (piRNA; 29-30&nbsp;nt) koja je aktivna u spolnim ćelijama i smatraju se da predstavljaju odbranu protiv transposona te igraju ulogu pri [[gametogeneza|gametogenezi]]<ref name=fruitfly_piRNA>{{cite journal|author=Horwich MD, Li C Matranga C, ''et al.''|title=The ''Drosophila'' RNA methyltransferase, DmHen1, modifies germline piRNAs and single-stranded siRNAs in RISC|journal=Current Biology|year=2007|volume=17|pages=1265-72}}</ref><ref>{{cite journal|author=Girard A, Sachidanandam R, Hannon GJ, Carmell MA|title=A germline-specific class of small RNAs binds mammalian Piwi proteins|journal=Nature|year=2006|volume=442|pages=199-202}}</ref>. Mnoge prokariotske ćelije imaju [[CRISPR]] RNK, regulatorni sistem sličan RNK interferenci<ref>{{cite journal|author=Horvath P, Barrangou R|title=CRISPR/Cas, the Immune System of Bacteria and Archaea|journal=Science|volume=327|pages=167|year=2010|url=http://www.sciencemag.org/cgi/content/abstract/327/5962/167}}</ref>.
 
Antisense RNK su široko rasprostranjene, najviše kao deregulatori gena, a nekoliko od njih su aktivatori transkripcije<ref>{{cite journal|author=Wagner EG, Altuvia S, Romby P|title=Antisense RNAs in bacteria and their genetic elements|journal=Adv Genet.|year=2002|volume=46|pages=361-98}}</ref>. Jedan od načina kako antisense RNK može djelovati je putem vezivanja na iRNK formirajući tako dvospiralnu zavojnicu RNK koja se enzimski degradira<ref>{{cite book|author=Gilbert SF|title=Developmental Biology|edition=7. izd.|publisher=Sinauer|pages=101-3|year=2003}} ISBN 0-87893-258-5</ref>. Postoji veliki broj dugih nekodnih RNK koje regulišu gene u eukariotskim ćelijama<ref>{{cite journal|author=Amaral PP, Mattick JS|title=Noncoding RNA in development|journal=Mammalian genome|volume= 19|issue=7-8|pages= 454|year=2008|month=oktobar}}</ref>, jedna od tih RNK je [[Xist]] koja prekriva jedan X [[hromozomkromosom]] u ženkama sisara i deaktivira ga<ref>{{cite journal|author=Heard E, Mongelard F, Arnaud D, ''et al.''|title=Human ''XIST'' yeast artificial chromosome transgenes show partial X inactivation center function in mouse embryonic stem cells|journal=Proc. Natl. Acad. Sci. USA|year=1999|volume=96|issue=12|pages=6841-46}}</ref>.
 
iRNK i sama može sadržavati regulatorne elemente, poput riboprekidača, u 5' neprevedenom regionu ili 3' neprevedenom regionu; ovi cis-regulatorni elementi reguliraju aktivnosti te iRNK<ref>{{cite journal|author=Batey RT|title=Structures of regulatory elements in mRNAs|journal=Curr. Opin. Struct. Biol.|volume=16|issue=3|pages=299-306|year=2006}}</ref>. Neprevedeni regioni također mogu sadržavati elemente koji reguliraju druge gene<ref>{{cite journal|author=Scotto L, Assoian RK|title=A GC-rich domain with bifunctional effects on mRNA and protein levels: implications for control of transforming growth factor beta 1 expression|journal=Mol. Cell. Biol.|volume=13|issue=6|pages=3588-97|year=1993|month=juni|url=http://mcb.asm.org/cgi/pmidlookup?view=long&pmid=8497272}}</ref>.
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