The present invention provides a nucleic acid such as a micro-RNA or a micro-RNA precursor, having a novel sequence. The nucleic acid of the present invention is useful for detecting the expression or a mutation of a micro-RNA, separating cells, suppressing the expression of a gene having a target sequence, screening for a substance that promotes or suppresses a function of a micro-RNA, and diagnosing or treating a disease caused by a mast cell abnormality, a disease caused by an abnormality of mesenchymal stem cell proliferation or differentiation, cancers, and a disease caused by abnormal proliferation of cells, tissue hyperplasia or the like.