Evidence for a Possible Direct Role of dCMP Hydroxymethylase in T4 Phage DNA Synthesis

Chiu, C S; Greenberg, Gordon R.

doi:10.1101/sqb.1968.033.01.041

Cited by 35 publications

(9 citation statements)

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“…However, other explanations would be considered. For example, dCMP-hydroxymethylase may be involved in base selection (13), and the enzyme which is synthesized by amC87 in the W3110 host may be particularly efficient in selecting hydroxymethylated precursor for incorporation into DNA. In the case of amE114, it is possible that the small amount of dCTPase which is synthesized by this mutant actively selects against the incorporation of dCTP.…”

Section: Resultsmentioning

confidence: 99%

Suppression of Amber Mutations of Bacteriophage T4 Gene 43 (DNA Polymerase) by Translational Ambiguity

Karam

O’Donnell

1973

J Virol

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The growth properties of twelve different amber (am) mutants of bacteriophage T4 gene 43 (DNA polymerase) were examined by using nonpermissive (su-) as well as permissive (su+) Escherichia coli hosts. It was found that most of these mutants were measurably suppressed in su-hosts by translational ambiguity (misreading of codons during protein synthesis). The ability of these mutants to grow in response to this form of weak suppression probably means that the T4 gene 43 DNA polymerase can be effective in supporting productive DNA replication when it is supplied in small amounts. By similar criteria, studies with other phage mutants suggested that the products of T4 genes 62 (uncharacterized), 44 (uncharacterized), 42 (dCMP-hydroxymethylase), and 56 (dCTPase) are also effective in small amounts. Some T4 gene products, such as the product of gene 41 (uncharacterized), seem to be partially dispensable for phage growth since am mutants of such genes do propagate, although weakly, in streptomycinresistant su-hosts which appear to have lost the capacity to suppress am mutations by ambiguity.

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Section: Resultsmentioning

confidence: 99%

Suppression of Amber Mutations of Bacteriophage T4 Gene 43 (DNA Polymerase) by Translational Ambiguity

Karam

O’Donnell

1973

J Virol

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“…We propose that dnaA has at least two functions: one the active function in initiation of rounds of replication and a second function as a component, perhaps structural, of the replication complex in which it associates with many, if not all, of the replication factors. Replication complexes have been proposed previously for T4 and Escherichia coli (3,10,11), and the observations of Bagdasarian et al (1) and Wechsler and Zdzienicka (15) on suppressors of dnaA mutations can be explained in terms of replication complexes.…”

mentioning

confidence: 65%

Interactions of DNA replication factors in vivo as detected by introduction of suppressor alleles of dnaA into other temperature-sensitive dna mutants

Blinkowa

Walker

1983

J Bacteriol

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Suppressor mutations located within dnaA can suppress the temperature sensitivity of a dnaZ polymerization mutant, indicating in vivo interaction of the products of these genes. The suppressor allele of dnaA [designated dnaA(SUZ, Cs)] could not be introduced, even at the permissive temperature, by transduction into temperature-sensitive (Ts) dnaC or dnaG recipients; it was transduced into dnaB(Ts) and dnaE(Ts) strains but at very low frequency. Recipient cells which were dnaA+ dnaE(Ts) were killed by the incoming dnaA(SUZ, Cs) allele, and it is presumed that combinations of dnaA(SUZ, Cs) with dnaB(Ts), dnaC(Ts), or dnaG(Ts) are lethal also. In one specific case, the lethality required the presence of three alleles: the incoming dnaA suppressor mutation, the resident dnaA+ gene, and the dnaB(Ts) gene. This was shown by the fact that dnaB(Ts) could readily be introduced into a dnaA(SUZ, Cs) dnaB+ recipient. That is, in the absence of dnaA+, the dnaA suppressor and dnaB(Ts) double mutant was stable. One model to explain these results proposes that the dnaA protein functions not only in initiation but also in the replication complex which contains multiple copies of dnaA and other replication factors.

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“…Our data establish that the failure of gene 42 mutants to synthesize DNA in plasmolyzed cells cannot be ascribed solely to a deficiency of growing chains to extend. Thus, one must postulate that P42 interacts directly with the replication apparatus, as proposed by Greenberg et al (3,28). DISCUSSION…”

Section: Iã Umentioning

confidence: 83%

Biochemistry of DNA-defective mutants of bacteriophage T4. VI. Biological functions of gene 42

North¹,

Stafford²,

Mathews³

1976

J Virol

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Bacteriophage T4 gene 1 and 42 amber mutants (defective in deoxynucleoside monophosphate kinase and deoxycytidylate hydroxymethylase, respectively) are able to synthesize DNA in cell-free lysates prepared as described by Barry and Alberts (1972), in contrast to their inability to do so in plasmolyzed and toluenized cell systems. Addition of extracts containing an active gene 1 or 42 product has no effect on synthesis in lysates defective in the respective gene. Thus, if these enzymes do play additional direct roles in replication, these roles are not manifest in the lysed-cell system. The gene 42 mutant am N122/m, a double mutant bearing an additional defect in DNA polymerase, is unable to synthesize DNA in these lysates. This inability is overcome by addition of extracts containing an active T4 DNA polymerase. m is a leaky amber mutation which reduces DNA polymerase activity to a very low level. However, this level is high enough to allow positive genetic complementation tests with gene 43 mutants. Two other gene 42 amber mutants contain additional defects: am 269 induces only half the normal level of DNA polymerase, and am C87 fails to induce a detectable level of thymidylate synthetase. These defects do not result from pleiotropic effects of the gene 42 mutations. In plasmolyzed cells, temperature-sensitive gene 42 mutants fail to synthesize DNA under conditions where replication forks and 5-hydroxymethyl-dCTP are present. This supports the idea that the gene 42 protein is directly involved in DNA synthesis.

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Evidence for a Possible Direct Role of dCMP Hydroxymethylase in T4 Phage DNA Synthesis

Cited by 35 publications

References 0 publications

Suppression of Amber Mutations of Bacteriophage T4 Gene 43 (DNA Polymerase) by Translational Ambiguity

Suppression of Amber Mutations of Bacteriophage T4 Gene 43 (DNA Polymerase) by Translational Ambiguity

Interactions of DNA replication factors in vivo as detected by introduction of suppressor alleles of dnaA into other temperature-sensitive dna mutants

Biochemistry of DNA-defective mutants of bacteriophage T4. VI. Biological functions of gene 42

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