MicroRNA and its Relationship with Tumor

miRNA is a kind of universally distributed non-coding small molecule RNA, of which thelength is about 22 nucleotides, miRNA plays a role in the negative regulation of gene expression, and thus af-fects physiological processes in cells. The abnormal expression of miRNA could lead to diseases, in particular,various tumors. In the past decades, most studies about tumorigenesis have focused on the mutations of eitheroncogenes or tumor suppressor genes; however, it was recently found that many of the incidences of cancerswere correlated with miRNA, which acts similarly as a tumor suppressor gane or an oncogene. The abnormai ex-pression of miRNA may be related to the highest probability of chromosomai fragile sites. In this review, we willdescribe the structures and functions of miRNA and discuss its relationship with carcinogenesis. Key words: miRNA ;  Tumor ;  Drosha ;  Dicer ;