Читать книгу Cell Biology - Stephen R. Bolsover - Страница 98

Once the synthesis of the DNA fragment is complete, the RNA primers must be replaced by deoxyribonucleotides. In prokaryotes the enzyme DNA polymerase I removes ribonucleotides using its 5′ to 3′ exonuclease activity and then uses its 5′ to 3′ polymerizing activity to incorporate deoxyribonucleotides. In this way, the entire RNA primer is replaced by DNA. Synthesis of the lagging strand is completed by the enzyme DNA ligase, which joins the DNA fragments together by catalyzing the formation of phosphodiester bonds between adjacent fragments.

Eukaryotic organisms use an enzyme called ribonuclease H to remove their RNA primers. These enzymes break phosphodiester bonds in an RNA strand that is hydrogen‐bonded to a DNA strand. Within each cell, ribonuclease H2 is involved in removing RNA primers during replication of nuclear genomic DNA and ribonuclease H1 is involved in removing RNA primers during replication of mitochondrial genomic DNA.