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G Mosig

Publications and source records attributed to G Mosig.

At least 55 records · Page 3Linked to original sources
PubMed1984

Light and Genetic Determinants in the Control of Specific Chloroplast Transcripts in Chlamydomonas reinhardtii.

We have looked for chloroplast genes whose expression is controlled by light by comparing the abundance of specific chloroplast transcripts in light-grown and dark-grown cells of Chlamydomonas reinhardtii. In addition, we have investigated whether genetic components influence expression of such genes.Northern blot analyses of specific separated transcripts showed that in certain strains (e.g. CC-278), several chloroplast transcripts from the Hpa II 5 region of the chloroplast chromosome were more abundant in dark-grown cells than in light-grown cells. The increased abundance of these Hpa II 5-specific transcripts was dependent on the genetic background: we have isolated mutants and we have found distantly related wild type strains which do not overaccumulate these transcripts in the dark.The strains which overaccumulated the Hpa II 5-specific transcripts, and only these strains, died after several cell divisions following transfer to the dark. Overaccumulation appears to be a necessary but not sufficient prerequisite for commitment to cell death in the dark.By analogy to bacterial systems, we speculate that a critical event associated with accumulation of one of these specific transcripts involves control at the level of transcription initiation or termination-antitermination.

Journal Article↗
PubMed1983

Early intermediates in bacteriophage T4 DNA replication and recombination.

We investigated, by density gradients and subsequent electron microscopy, vegetative T4 DNA after single or multiple infection of Escherichia coli with wild-type T4. Our results can be summarized as follows. (i) After single infection (i.e., when early intermolecular recombination could not occur), most, if not all, T4 DNA molecules initiated the first round of replication with a single loop. (ii) After multiple infection, recombinational intermediates containing label from both parents first appeared as early as 1 min after the onset of replication, long before all parental DNA molecules had finished their first round and before secondary replication was detectable. (iii) At the same time, in multiple infections only, complex, highly branched concatemeric T4 DNA first appeared. (iv) Molecules in which two loops or several branches were arranged in tandem were only found after multiple infections. (v) Secondary loops within primary loops were seen after both single and multiple infections, but they were rare and many appeared off center. Thus, recombination in wild-type T4-infected cells occurred very early, and the generation of multiple tandem loops or branches in vegetative T4 DNA depended on recombination. These results are consistent with the previous finding (A. Luder and G. Mosig, Proc. Natl. Acad. Sci. U.S.A. 79:1101-1105, 1982) that most secondary growing points of T4 are not initiated from origin sequences but from recombinational intermediates. By these and previous results, the various DNA molecules that we observed are most readily explained as intermediates in DNA replication and recombination according to a model proposed earlier to explain various other aspects of T4 DNA metabolism (Mosig et al., p. 277-295, in D. Ray, ed., The Initiation of DNA Replication, Academic Press, Inc., New York, 1981).

DNA Replication↗
PubMed1982

Two alternative mechanisms for initiation of DNA replication forks in bacteriophage T4: priming by RNA polymerase and by recombination.

We show that bacteriophage T4 has two alternative mechanisms to initiate DNA replication; one dependent on Escherichia coli RNA polymerase (RNA nucleotidyltransferase, EC 2.7.7.6), and one dependent on general recombination. Continued DNA synthesis under recombination-defective conditions was sensitive to rifampin, an inhibitor of RNA polymerase. On the other hand, DNA synthesis accelerated in spite of the present of rifampin if recombination occurred.

DNA Replication↗
PubMed1981

Semiconservative DNA replication is initiated at a single site in recombination-deficient gene 32 mutants of bacteriophage T4.

We have investigated, by electron microscopy, replicative intermediate produced early after infection of Escherichia coli with two phage T4 gene 32 mutants (amA453 and tsG26) which replicate their parental DNA but are defective in secondary replications and in moderating the activities of recombination nucleases. Under conditions completely restrictive for progeny production, both of these mutant produced replicative intermediates, each containing a single internal loop. Both branches of these loops were double stranded; i.e., both leading and lagging strands were synthesized. The replicative intermediates of these mutants qualitatively and quantitatively resembled early replicating wild-type T4 chromosomes after solitary infection of E. coli. However, in contrast to intracellular wild-type T4 DNA isolated from multiple infection, the mutant DNAs showed neither multiple branches nor multiple tandem loops. These results demonstrate that a truncated gene 32 protein which consists of less than one-third of the wild-type T4 helix-destabilizing protein can facilitate the functions of T4 replication proteins, specifically those of T4 DNA polymerase and priming proteins. Our results also support the hypothesis that the generation of multiple tandem loops or branches in vegetative T4 DNA depends on recombination (Mosig et al., in B. Alberts, ed., Mechanistic Studies of DNA Replication and Genetic Recombination, p. 527-543, Academic Press, Inc., New York, 1980).

DNA Replication↗
PubMed1981

Interactions between the maturation protein gp17 and the single-stranded DNA binding protein gp32 initiate DNA packaging and compete with initiation of secondary DNA replication forks in phage T4.

Since T4 DNA, which is being packaged is actively replicating and recombining, we have asked whether replication and recombination proteins interact with maturation proteins. We report here on genetic evidence for interaction of the single-stranded DNA binding protein gp32 with the maturation protein gp17. Based on these and other results we suggest a model in which DNA packaging is initiated from recombinational intermediates.U

Carrier Proteins↗
PubMed1977

Multiple interactions of a DNA-binding protein in vivo. III. Phage T4 gene-32 mutations differentially affect insertion-type recombination and membrane properties.

We have investigated in in vivo roles of T4 gene-32 protein in recombination. We have studied the effects of gene-32 mutations under conditions that allow normal DNA replication and are permissive for progeny production. Under these conditions, certain gene-32 mutations specifically reduce insertion-type (short-interval) recombination but none affect crossover-type (long-interval) recombination (see Figure 5). Heterozygote frequencies in all gene-32 mutants are similar to or higher than in a gene-32+ background and are not correlated with recombination deficiencies. "Recombination-deficient" alleles are dominant or codominant over the "recombination-proficient" gene 32 mutation tsL171. This explains apparent discrepancies between a gene-32 map deduced from two-factor crosses and the map derived from three-factor crosses. We have also found that the "recombination proficient" mutation tsL171 and it homdoalleles suppress the characteristic plaque morphology of rII mutants. Under restrictive conditions, tsL171 is partially suppressed by rII mutations, which allow the use of host ligase in recombination. Our present and previous results are discussed in terms of current recombination models. We conclude that gene-32 protein functions in recombination by forming a complex with DNA, with recombination enzymes and with membrane components. Since gene-32 protein interacts with many components of this recombination complex, gene-32 mutations may differentially affect various recombination steps.

Alleles↗
PubMed1976

Gene 32 protein of bacteriophage T4 moderates the activities of the T4 gene 46/47-controlled nuclease and of the Escherichia coli RecBC nuclease in vivo.

Genes 46 and 47 of phage T4 control a nuclease that is required for genetic recombination and may act similarly to the Escherichia coli RecBC nuclease. In vivo, the nucleolytic activities of both of these nucleases must be moderated so that recombining DNA intermediates are not destroyed. We conclude from our present experiments that the phage T4 gene 32 protein, specifically its C-terminal domain, participates in such moderation. We have investigated DNA degradation in different gene 32 and gene 32/46 mutants under conditions that are completely restrictive for progeny production in all the mutants. Under these conditions, DNA of those gene 32 mutants in which the C-terminal domain of the protein is not synthesized or is modified is degraded to acid-soluble material. T4 gene 46 or E. coli recB mutations reduce such degradation; together they abolish it completely. By contrast, single gene 32 mutants which produce an unaltered C-terminal domain show little or no degradation of their DNA. Residual protection against nucleases is unrelated to residual primary DNA replication or to overproduction of the mutant peptides in the different gene 32 mutants.

Coliphages↗
PubMed1975

Genetic evidence for an additional function of phage T4 gene 32 protein: interaction with ligase.

Gene 32 of bacteriophage T4 is essential for DNA replication, recombination, and repair. In an attempt to clarify the role of the corresponding gene product, we have looked for mutations that specifically inactivate one but not all of its functions and for compensating suppressor mutations in other genes. Here we describe a gene 32 ts mutant that does not produce progeny, but in contrast to an am mutant investigated by others, is capable of some primary and secondary DNA replication and of forming "joint" recombinational intermediates after infection of Escherichia coli B at the restrictive temperature. However, parental and progeny DNA strands are not ligated to covalently linked "recombinant" molecules, and single strands of vegetative DNA do not exceed unit length. Progeny production as well as capacity for covalent linkage in this gene 32 ts mutant are partially restored by additional rII mutations. Suppression by rII depends on functioning host ligase [EC 6.5.1.2; poly(deoxyribonucleotide):poly(deoxyribonucleotide) ligase (AMP-forming, NMN-forming)]. This gene 32 ts mutation (unlike some others) in turn suppresses the characteristic plaque morphology of rII mutants. We conclude that gene 32 protein, in addition to its role in DNA replication and in the formation of "joint" recombinational intermediates, interacts with T4 ligase [EC 6.5.1.1; poly(deoxyribonucleotide):poly(deoxyribonucleotide) ligase (AMP-forming)] when recombining DNA strands are covalently linked. The protein of the mutant that we describe here is mainly defective in this interaction, thus inactivating T4 ligase in recombination. Suppressing rII mutations facilitate substitution of host ligase. There is suggestive evidence that these interactions occur at the membrane.

Binding Sites↗
PubMed1972

Coordinate variation in lengths of deoxyribonucleic acid molecules and head lengths in morphological variants of bacteriophage T4.

We have investigated three classes of small bacteriophage T4 particles which differ from normal T4 particles in length of their deoxyribonucleic acid (DNA), in head length, in protein content, and in density. The different particles contain DNA molecules measuring 0.90, 0.77, or 0.67, respectively, of the normal T4 length. An additional class of viable particles contains DNA molecules of 1.1 unit length. These discrete differences in DNA length correspond to discrete differences in length (but not width) of the respective heads and are roughly proportional to the resulting differences in head volumes. The measured relative dimensions of the different heads fit best the relative dimensions predicted by a quasi-icosahedral model in which the smallest T4 head corresponds to an icosahedron with a triangulation number T = 21. The mid-portion of this structure is thought to be elongated by adding successive rows of gene 23 protein hexamers, the normal T4 head having three added rows. Different mutants produce small particles of the three classes in varying proportions, but no mutant produces exclusively particles of a single class. Particles of each class, with indistinguishable DNA content, show additional minor differences in protein content, as measured by differences in buoyant density and in the relative ratio of (32)P to (35)S.

Centrifugation, Density Gradient↗
PubMed1972

Bacteriophage T4 head models based on icosahedral symmetry.

In an accompanying paper, the coordinate variation in lengths of deoxyribonucleic acid molecules and head lengths in morphological variants of bacteriophage T4 is discussed. As an appendix to that report, models for the T4 phage heads, based on previously developed architectural principles for assembly of icosahedral virus, are compared with the data for the best fit.

Coliphages↗