Question

Identification of protein components involved in DNA synthesis

1. Temperature sensitive mutants:
____ ____ mutants; replication at permissive conditions but fail to function at nonpermissive conditions (high temp.; 42°C).
In E. coli, identified ___ named "__" genes.

2. dna genes:
a. Quick-stop mutants: immediate stop in replication; ____ ____ defective & defects in precursors.
b. Slow-stop mutants: defective in ____ at the origin (smaller class). (DnaA, SeqA)

Answer 1

The enzyme most likely to be mutated when the joining of Okazaki fragments is impaired is DNA ligase. This enzyme is responsible for connecting the short DNA fragments on the lagging strand during DNA replication.

Step-by-step explanation:

You isolate a cell strain in which the joining of Okazaki fragments is impaired and suspect that a mutation has occurred in an enzyme found at the replication fork. The enzyme most likely to be mutated in this case would be DNA ligase. This enzyme is crucial for sealing the nicks between Okazaki fragments on the lagging strand during DNA replication, thereby creating a continuous DNA strand. Mutations in DNA ligase can result in slow growth, similar to that observed by Okazaki and colleagues in T4 phage mutant studies. Among the identified mutants, those affecting the ability to replicate at non-permissive conditions are called temperature sensitive mutants. In E. coli, DNA genes are often targets for discovering replication mutants, which can be classified as either quick-stop mutants, with immediate replication stoppage due to DNA polymerase defects or precursor defects, or slow-stop mutants, which have defects in initiation at the origin of replication.