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Chromosomal basis of the merozygosity in a partially deploid mutant of Pneumococcus
Abstract:
A sulfonamide-resistant mutant of pneumococcus, sulr-c, displays a genetic instability, regularly segregating to wild type. DNA extracts of derivatives of the strain possess transforming activities for both the mutant and wild-type alleles, establishing that the strain is a partial diploid. The linkage of sulr-c to strr-61, a stable chromosomal marker, was established, thus defining a chromosomal locus for sulr-c. DNA isolated from sulr-c cells transforms two mutant recipient strains at the same low efficiency as it does a wild-type recipient, although the mutant property of these strains makes them capable of integrating classical "low-efficiency" donor markers equally as efficiently as "high efficiency" markers. Hence sulr-c must have a different basis for its low efficiency than do classical low efficiency point mutations. We suggest that the DNA in the region of the sulr-c mutation has a structural abnormality which leads both to its frequent segregation during growth and its difficulty in efficiently mediating genetic transformation.
Insights
A pneumococcus mutant (sulr-c) shows genetic instability and partial diploidy. Its low transformation efficiency suggests a DNA structural abnormality, not a typical mutation.
Area of Science:
- Microbial Genetics
- Bacterial Transformation
- Molecular Biology
Background:
- Pneumococcus harbors genetic instability in the sulfonamide-resistant mutant sulr-c.
- This mutant strain exhibits regular segregation to the wild type.
- Understanding the genetic basis of drug resistance and instability is crucial in microbial research.
Purpose of the Study:
- To investigate the genetic instability and transformation characteristics of the pneumococcus sulr-c mutant.
- To determine the chromosomal locus of the sulr-c mutation.
- To elucidate the underlying cause of the mutant's low genetic transformation efficiency.
Main Methods:
- Genetic transformation assays using DNA extracts from sulr-c derivatives.
- Analysis of transforming activities for both mutant and wild-type alleles.
- Linkage analysis with a stable chromosomal marker (strr-61) to define the sulr-c locus.
Main Results:
- DNA extracts demonstrated transforming activity for both mutant and wild-type alleles, indicating partial diploidy.
- The sulr-c mutation was mapped to a specific chromosomal locus linked to strr-61.
- Low transformation efficiency of sulr-c was observed across both mutant and wild-type recipients, distinct from classical low-efficiency mutations.
Conclusions:
- The sulr-c mutant is a partial diploid with a defined chromosomal locus.
- The low transformation efficiency is likely due to a structural abnormality in the DNA region of the sulr-c mutation.
- This structural abnormality may also underlie the strain's genetic instability and frequent segregation.