Mikrorna'ların dizi bileşenleri ve ifade düzeylerinin araştırılması

ABSTRACTEVALUATION OF MICRORNA SEQUENCE COMPOSITION ANDEXPRESSIONKoray Doğan KayaM.S. in Molecular Biology and GeneticsSupervisors: Asst. Prof. Dr. Özlen Konu, Asst. Prof. Dr. M. Cengiz YakıcıerAugust 2005, 70 pagesMicroRNAs are small, ~22nt in length, ribonucleic acids, which bind to3?UTR regions of mRNAs by base complementation. They play crucial roles in theregulation of embryonic development, and in many cellular events such asproliferation, apoptosis, and differentiation. Previous bioinformatics studies haveconcentrated on the prediction and transcriptional regulation of miRNA and targetsequences. In the present study, the dinucleotide and trinucleotide composition ofpremature and mature microRNAs were evaluated. Moreover, the significance ofbiased dinucleotide usage was determined using a randomization approach. Thescarcity of CpG motif, a generalized characteristic of mammalian genomes, wasfound to be a prominent feature also in miRNA sequences. Furthermore, miRNAsthat contain one or more CpG motif(s) were found to be expressed at relatively lowerlevels in multiple adult tissues, except in the brain, based on existing human andmouse microarray datasets. The implications of the negative correlation between theCpG usage and the average expression level of miRNAs were discussed in the lightof mammalian immune defenses and methylation characteristics.Keywords: microRNA, microarray, bioinformatics, CpG dinucleotide, randomization.