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Table 1 Different types of circRNAs

From: Circular RNAs’ cap-independent translation protein and its roles in carcinomas

Categories Composition characteristics Main positioning The main function Ref.
CiRNAs Intron splicing Nucleus Participate in regulating the expression of its parental genes [20]
EcircRNAs Exon splicing Cytoplasm As a sponge of miRNA or interact with RBPs [34]
EIciRNAs Contains introns and exons Nucleus Promote the transcription of its host gene by interacting with U1 small nuclear ribonucleoprotein (snRNP) [22]
f−circRNAs Linear fusion transcript derived from genome rearrangement (chromosomal translocation) Cytoplasm and nucleus Contribute to cell transformation, promote cell viability and drug resistance after treatment, and have tumor-promoting properties in in vivo models [23]
rt− circRNAs Coding exons of two adjacent and similarly oriented genes (read-through transcription) Cytoplasm To be elucidated, it may be a mechanism of gene regulation in a specific environment; it may be a mechanism of protein complex evolution [26]
mecciRNAs Mitochondrial Genome Mitochondria inside and outside As a molecular chaperone, it helps to fold nuclear-encoded proteins and facilitate their entry into the mitochondria. [45]