Classification of Non-coding RNAs. They were classified into housekeeping and regulatory RNAs according to their functions. Housekeeping ncRNAs consist of carrier RNA and ribosomal RNA. On the other hand, regulatory RNAs contain small non-coding RNAs (sncRNAs) and long non-coding RNAs (lncRNAs). Small ncRNAs that vary in a base range of approximately 15–40; microRNAs (miRNA), small nucleolar RNAs (snoRNAs), small inhibitory RNAs (siRNAs), small nuclear RNAs (snRNAs), and RNAs interacting with PIWI (piRNAs).