Question

Why are origins of replication (ORI)populated by that many protein complexes?

How can microRNAs interfere with gene expression (mRNA abundance)of a target gene?

please answer both

Answer 1

1. Origin of replication (ORI) is the region where the process of replication starts. To retain genome integrity , it must be ensured that DNA is replicated only once before cell division occurs. It is being monitored by a process called replication or licensing . A licencing factor is a protein complex that licence or permits an origin of replication to begin DNA replication at that origin. Origin recognition complex (ORC) is a 6 subunit DNA binding complex and a key participant for eukaryotic DNA replication that is constantly bound to chromatin at replication origins during the whole of the cell cycle.Therefore, initiator proteins of licensing includes, Origin Recognition Complex (ORC), Cdc6/18, Cdt1 and the MCM complex. At the completion of mitosis, the MCM complex is loaded on to the chromosome with the help of ORC, Cdc6/18 and Cdt1, and the origin site becomes licensed for replication.

2. miRNAs (microRNAs) are short non-coding RNAs involved in post -transcriptional regulation of gene expression. The transalational silencing is generally initiated by binding of miRNA to the 3'-UTR of their target mRNAs and supress protein synthesis by destabilizing the mRNA. They act as locks to the target mRNA via complementary base-pairing within mRNA molecules and stop their transalation into proteins.  However, the exact mechanism is yet to be fully elucidated, but recent studies suggests that the stage of translation which is supressed by miRNAs is reliant on the promoter used for transcription.