High Quality Content by WIKIPEDIA articles! The miR-15 microRNA precursor family are small non-coding RNA genes that regulate gene expression. The family includes the related mir-15a and mir-15b sequences. In humans miR-15a and miR-16 are clustered within 0.5 kilobases at 13q14. This region has been shown to be deleted in more than half of B-cell chronic lymphocytic leukemias (CLL). Both miR-15a and miR-16 are deleted or down-regulated in more than two thirds of CLL cases. The mature sequence is excised from the 5` arm of the hairpin. In mouse lymphoid development, the miR-15 family has been implicated in turning down cell cycle by down-regulation of check-point genes.