Other Enzymes That Act on DNA

Many other enzymes modify DNA and degrade it in various ways. In the next chapter we discuss some of those enzymes that have been particularly useful in DNA manipulations. In Supplement 3 (Immunobiology) we discuss DNA splicing operations that are essential for assembling complex antibody genes prior to their expression. 

This chapter deals with reactions involved in DNA synthesis, degradation, repair, and recombination. The chief points to remember are as follows. 

DNA replication proceeds by the synthesis of one new strand on each of the parental strands. This mode of replication is called semiconservative, and it appears to be universal. DNA synthesis initiates from a primer at a unique point on a prokaryotic template such as the E. coli chromosome. From the initiation point, DNA synthesis proceeds bidirectionally on the circular bacterial chromosome. The bidirectional mode of synthesis is not followed by all chromosomes. For some chromosomes, usually small in size, replication is unidirectional. 

Many proteins are required for DNA synthesis and chromosomal replication. These include polymerases helicases, which unwind the parental duplex enzymes that fill in the gaps and join the ends in the case of lagging-strand synthesis enzymes that synthesize RNA primers at various points along the DNA tem- 

mutations have been isolated in the genes encoding a number of these enzymes. Many of these mutations are conditional because the functional enzymes involved are required for DNA synthesis and cell viability. Mutants carrying mutationally altered proteins have been important in confirming their roles predicted from cell-free studies. 

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A number of other enzymes that act on DNA and RNA are an important part of recombinant DNA tech-nology. Many of these are referred to in this and subsequent chapters (Table 40-3). 

Bacterial Reverse Transcriptase Catalyzes Synthesis of a DNA-RNA Molecule Telomerase Facilitates Replication at the Ends of Eukaryotic Chromosomes Other Enzymes That Act on DNA... 

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