During the processing of hnRNA to active mRNA the phenomenon involved in the breakdown and making of phosphodiester bonds in the RNA is called 

During the processing of hnRNA to active mRNA, the introns are removed by breaking phosphodiester bonds at the junction of exon and intron regions of RNA and the exons are attached by forming phosphodiester bonds. This process is brought about by spliceosomes and process is called splicing.