Final answer:
In yeast, exonucleases like Exo1 and Dna2 digest ssDNA, being part of DNA repair and replication processes. Restriction endonucleases serve as a defense against viruses, cleaving foreign DNA at specific sequences. While some repair enzymes are essential, others can be safely knocked out without being lethal.
Step-by-step explanation:
In yeast, the exonucleases that are known to digest single-stranded DNA (ssDNA) include Exo1 and Dna2. These enzymes participate in DNA metabolism processes such as replication and repair. In the context of defense against viruses, yeast cells and bacteria use restriction endonucleases as a protective mechanism. These enzymes recognize and cleave viral DNA at specific sequences, thereby defending the host cell against viral invasion.Restriction endonucleases in yeast are also crucial for research applications, such as DNA fingerprinting and cloning. They have been used to detect genetic mutations and establish parentage or forensic evidence. Certain enzymes are critical for cell survival and reproduction; thus, knocking them out could be lethal.
On the other hand, there are some non-essential genes encoding DNA repair enzymes that can be knocked out without being fatal to the cell, as they have backup mechanisms or are only required under specific stress conditions.Still, the degree of redundancy within the DNA repair mechanisms in yeast means that caution should still be exercised when considering the knockouts of any such genes, and thorough analysis of the yeast's ability to maintain genomic integrity after such a knockout should be conducted.