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N Sternberg

Publications and source records attributed to N Sternberg.

At least 73 records · Page 4Linked to original sources
PubMed1981

A novel role for site-specific recombination in maintenance of bacterial replicons.

If daughter copies of unit-copy replicons recombine with each other, a replicon dimer results that cannot be partitioned equally to daughter cells at cell division. We present evidence that dimer formation interferes with plasmid equipartition in the case of a miniplasmid derived from the unit-copy plasmid prophage of bacteriophage P1. Asymmetric partition occurs, leading to a relatively high rate of loss of the plasmid from the growing population. In contrast, the wild-type P1 plasmid is maintained very efficiently in host cells. We show that this efficient maintenance is due to the presence of the loxP-cre site-specific recombination system present on the intact P1 plasmid. This system promotes rapid recombination between two loxP sites on dimer molecules, resolving them into monomeric substrates for proper partition. We suggest that bacterial replicons that are maintained with great accuracy in recombination-proficient cells might also encode high-efficiency recombination systems.

Base Sequence↗
PubMed1979

A simple technique for the isolation of deletion mutants of phage lambda.

We describe a simple technique for isolating deletion mutants of phage lambda and use it to dissect a cloned fragment of foreign DNA. The technique is based on our previous finding that the normally essential product of lambda head gene D is dispensible for phage growth if the DNA content of the phage is less than 82% that of lambda wild-type (Sternberg and Weisberg, 1977). A significant fraction of the few phage that form plaques when a D amber mutant is plated on a nonsuppressing host contains deletions that reduce the phage chromosome size to less than 82% that of wild-type. It is possible to isolate deletions ranging in size from less than 1.5 kb to 14 kb (3 to 27% of wild-type lambda), and the size range can be restricted by an appropriate choice of the DNA content of the starting phage. This method, unlike the older EDTA or heat resistance methods, permits the scoring of deletions because of the absence of phenotypic variants. We investigated the effect of several host and phage mutations on deletion frequency and type and have determined that a host polA mutation increases the frequency of deletions about 30-50-fold without changing the type of deletions. A host mutD mutation or thymine deprivation increases deletion frequency about 10-fold. In contrast, a host ligts mutation has no effect on the frequency of deletions. We have also determined that the size of the smallest lambda chromosome packageable in a plaque-forming phage particle is 72-73% that of lambda wild-type.

Bacteriophage lambda↗
PubMed1979

Analysis of coliphage lambda mutations that affect Q gene activity: puq, byp, and nin5.

We describe in this paper the isolation and characterization of a class of mutations, designated puq, that allow phage lambda to grow better under conditions that limit the synthesis of the phage Q gene product. These mutations were located between phage genes P and Q, a region of the lambda chromosome containing two gene N-independent mutations, nin5 and byp, that we also show to be puq mutations. Whereas the puq-3 and puq-16 mutations probably map under the nin5 deletion, the byp mutation maps between this deletion and the Q lambda-Q phi 80 crossover point. These mutations likely act by increasing the synthesis of the Q gene product. We demonstrate that the clear-plaque phenotype and reduced lysogenization frequency of byp mutants depend on increased Q gene activity. The significance of these results in understanding how transcription proceeds through the P-Q region of the lambda genome is discussed.

Bacteriophage lambda↗
PubMed1978

Analysis of bacteriophage P1 immunity by using lambda-P1 recombinants constructed in vitro.

We describe the dissection and reconstruction of a complex control circuit, the P1 immunity system, by a method that involves inserting EcoRI-generated fragments of P1 DNA into lambda vectors that can then be sequentially inserted into a bacterial cell. Using these techniques we have isolated lambda-P1 hybrid phages that express the products of P1 genes c1, c4, ant, and ban and, in appropriately constructed lysogens, confirmed the roles played by the first three of these products in phage immunity. In addition we have localized to particular P1 fragments the sites requisite for expression and repression of these gene products. The analysis leads to the conclusion that gpant acts in trans to antagonize repression mediated by gpc1, in support of one of two proposed models for gpant action. Moreover, two features of the immunity system are revealed: (i) a hitherto unknown component that effects gpc1 repression; and (ii) an unexpected ability of gpc4 to channel a superinfecting c1+ phage into the lysogenic state, which suggests that gpc4 activity regulates the establishment phase of lysogeny.

Alleles↗