Noncoding RNAs in gastric cancer: Research progress and prospects

Table 1 Major classification of human genomic noncoding RNAs

RNA type	Symbol	Length (nt)	Function
Housekeeping ncRNAs
Transfer RNAs	tRNA	73-94	Connect amino acids with mRNA
Ribosomal RNAs	rRNA	121-5070	Component of ribosomes
Small nuclear RNAs	snRNA	Approximately 150	Assemble with proteins into spliceosomes to remove introns during mRNA processing
Small nucleolar RNAs	snoRNA	70-200	Guide modifications of other ncRNAs, alternative splicing; or function as miRNA
Telomerase RNAs	TERC	451	Provide template for de novo synthesis of telomeric DNA
Ribonuclease P	RPPH1	341	RNA component of ribonuclease P
Regulatory ncRNAs
Small interfering RNAs	siRNA	21-22	Silencing genes in a sequence-specific manner
MicroRNAs	miRNA	20-23	Regulating genes expression
Piwi-interacting RNA	piRNA	25-33	Silence transposons during spermatogenesis
Promoter-associated short RNAs	paRNA	< 200	Regulating gene expression by gene promoter
Long non-coding RNAs	lncRNA	> 200	Various

ncRNAs: Noncoding RNAs; piRNAs: PIWI-interacting RNAs; lncRNAs: Long ncRNAs.