DNA packaging by lambda-like bacteriophages: mutations broadening the packaging specificity of terminase, the lambda-packaging enzyme.
Genetics
; 184(1): 43-52, 2010 Jan.
Article
en En
| MEDLINE
| ID: mdl-19841094
ABSTRACT
The DNA-packaging specificities of phages lambda and 21 depend on the specific DNA interactions of the small terminase subunits, which have support helix-turn-recognition helix-wing DNA-binding motifs. lambda-Terminase with the recognition helix of 21 preferentially packages 21 DNA. This chimeric terminase's ability to package lambdaDNA is reduced approximately 20-fold. Phage lambda with the chimeric terminase is unable to form plaques, but pseudorevertants are readily obtained. Some pseudorevertants have trans-acting suppressors that change codons of the recognition helix. Some of these codons appear to remove an unfavorable base-pair contact; others appear to create a novel nonspecific DNA contact. Helper-packaging experiments show that these mutant terminases have lost the ability to discriminate between lambda and 21 during DNA packaging. Two cis-acting suppressors affect cosB, the small subunit's DNA-binding site. Each changes a cosB(lambda)-specific base pair to a cosB(21)-specific base pair. These cosB suppressors cause enhanced DNA packaging by 21-specific terminase and reduce packaging by lambda-terminase. Both the cognate support helix and turn are required for strong packaging discrimination. The wing does not contribute to cosB specificity. Evolution of packaging specificity is discussed, including a model in which lambda- and 21-packaging specificities diverged from a common ancestor phage with broad packaging specificity.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
ADN Viral
/
Bacteriófago lambda
/
Empaquetamiento del ADN
/
Endodesoxirribonucleasas
/
Mutación
Idioma:
En
Revista:
Genetics
Año:
2010
Tipo del documento:
Article
País de afiliación:
Estados Unidos