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S Hattman

Publications and source records attributed to S Hattman.

At least 73 records · Page 4Linked to original sources
PubMed1978

Comparative study of DNA methylation in three unicellular eucaryotes.

We have analyzed the nature/content of methylated bases in the nuclear DNA of three unicellular eucaryotes. The pattern of methylation was different for each of the three organisms studied: Saccharomyces cerevisiae contained only 5-methylcytosine; Tetrahymena pyriformis contained only N6-methyladenine; and Chlamydomonas reinhardi contained both modified bases.

Adenine↗
PubMed1977

Partial purification of the Escherichia coli K-12 mec+ deoxyribonucleic acid-cytosine methylase: in vitro methylation completely protects bacteriophage lambda deoxyribonucleic acid against cleavage by R-EcoRII.

A procedure is described for the partial purification of the deoxyribonucleic acid (DNA)-cytosine methylases controlled by the RII plasmid and by the Escherichia coli mec+ gene. The two enzymes exhibit similar but distinct chromatographic behavior on diethylaminoethyl-cellulose and phosphocellulose. Preliminary studies on the two methylases indicate that they are indistinguishable with respect to their Km for S-adenosylmethionine and their pH (in tris (hydroxymethyl)aminomethane buffer) and NaCl concentration optima. In vitro methylation of various phage lambda DNA substrates by the mec'r RII enzyme modifies the DNA to a form that is completely resistant to double-stranded cleavage by the RII restriction endonuclease (R-EcoRII). These results are consistent with our earlier proposal that the mec8ethylase recognizes RII host specificity sites.

Coliphages↗
PubMed1976

In vivo methylation by Escherichia coli K-12 mec+ deoxyribonucleic acid-cytosine methylase protects against in vitro cleavage by the RII restriction endonuclease (R. Eco RII).

We have analyzed the susceptibility of the deoxyribonucleic acid (DNA) of phage fd replicative form (RF) and of Escherichia coli to in vitro cleavage by purified RII restriction endonuclease (R. Eco RII). The results are summarized as follows: (i) fd, mec- RFI, isolated from infected E. coli K-12 mec- bacteria (a mutant strain lacking DNA-cytosine methylase activity), is cleaved into at least two fragments, whereas fd. mec+ RFI, isolated from the parental mec+ strain, is not cleaved. (ii) E. coli mec- DNA is extensively degraded, whereas mec+ DNA-cytosine methylase acts as an RII modification enzyme.

Coliphages↗
PubMed1976

Salmonella typhimurium SA host specificity system is based on deoxyribonucleic acid-adenine methylation.

We have determined the nature of the deoxyribonucleic acid (DNA) modification governed by the SA host specificity system of Salmonella typhimurium. Two lines of evidence indicate that SA modification is based on methylation of DNA-adenine residues. (i) The SA+ locus of Salmonella was transferred into Escherichia coli B, a strain that does not contain 5-methylcytosine in its DNA; although the hybrid strain was able to confer SA modification, its DNA still did not contain 5-methylcytosine. (ii) the N6-methyladenine content of phage L DNA was measured after growth in various host strains; phage lacking SA modification contained fewer N6-methyladenine residues per DNA. We also investigated the possibility, suggested by others (32), that SA modification protects phage DNA against restriction by the RII host specificity system. Phages lambda, P3, and L were grown in various SA+ and SA- hosts and tested for their relative plating ability on strains containing or lacking RII restriction; the presence or absence of SA modification had no effect on RII restriation. In vitro studies revealed, however, that Salmonella DNA is protected against cleavage by purified RII restriction endonuclease (R-EcoRII). This protection is not dependent on SA modification; rather, it appears to be due to methylation by a DNA-cytosine methylase which has overlapping specificity with the RII modification enzyme, but which is not involved in any other known host specificity system.

Adenine↗
PubMed1974

Mutants of the N-3 R-factor conditionally defective in hspII modification and deoxyribonucleic acid-cytosine methylase activity.

The N-3 drug resistance (R) factor specifies a deoxyribonucleic acid (DNA)-cytosine methylase and a DNA restriction-modification (hspII) system. We have isolated three independent mutants that are conditionally defective in their ability to modify bacteriophage lambda and to methylate DNA-cytosine residues. The ratio of 5-methylcytosine to N(6)-methyladenine in bacterial DNA and in the DNA of phages lambda and fd was determined after labeling with [methyl-(3)H]methionine at various growth temperatures. Although the ability of the wild-type N-3 factor to modify phage lambda and to methylate DNA-cytosine residues was unaffected with increasing temperature, two of the mutants exhibited a parallel loss in modification and cytosine methylation ability. The ability of the third mutant to carry out these functions was dependent on the presence or absence of an amber suppressor mutation in the host genome. These results offer further support for the notion that hspII modification is mediated by a DNA-cytosine methylase. Evidence is also presented that the modification methylase is responsible for the in vivo methylation of phage fd DNA (which is not subject to hspII restriction in vivo).

Alanine↗
PubMed1973

( 6 N)methyl adenine in the nuclear DNA of a eucaryote, Tetrahymena pyriformis.

DNA isolated from macronuclei of the ciliate, Tetrahymena pyriformis, has been found to contain [(6)N]methyl adenine (MeAde); this represents the first clear demonstration of significant amounts of MeAde in the DNA of a eucaryote. The amounts of macronuclear MeAde differed slightly between different strains of Tetrahymena, with approximately 0.65-0.80% of the adenine bases being methylated. The MeAde content of macronuclear DNA did not seem to vary in different physiological states. The level of MeAde in DNA isolated from micronuclei, on the other hand, was quite low (at least tenfold lower than in macronuclear DNA).

Adenine↗
PubMed1973

Isolation of a mutant of Escherichia coli defective in cytosine-specific deoxyribonucleic acid methylase activity and in partial protection of bacteriophage lambda against restriction by cells containing the N-3 drug-resistance factor.

A mutant (designated mec(-)) of Escherichia coli F(+) 100 endo I(-)su(+) r(K) (-)m(K) (+) has been isolated which is defective in cytosine-specific deoxyribonucleic acid (DNA) methylase activity. The DNA of this mutant, as well as the DNA of phages lambda and fd propagated in it, is virtually devoid of 5-methyl-cytosine (MeC); in contrast, the mutation has no significant effect on the level of N(6)-methyladenine in DNA. Phage lambda grown on the mec(-) mutant is more strongly restricted by N-3-containing cells than is lambda grown on the mec(+) parent. These results suggest that methylation of certain cytosine residues by the E. coli K-12 enzyme partially protects lambda DNA from either the N-3 restriction nuclease or against secondary degradation subsequent to N-3-specific degradation. Analysis of the MeC level in viral and cellular DNA obtained from mec(+), mec(+) (m(N3) (+)), and mec(-) (m(N3) (+)) strains has led to the conclusion that the R-factor controlled DNA-cytosine methylase may be capable of methylating a sequence(s) which is a substrate for the K-12 enzyme.

Adenine↗
PubMed1972

Methylation of cytosine residues in DNA controlled by a drug resistance factor (host-induced modification-R factors-N 6 -methyladenine-5-methylcytosine).

The proportion of 5-methylcytosine (5MeCyt) and 6-methylaminopurine (N(6)-methyladenine, 6MeAde) in bacteriophage P22 DNA was analyzed as a function of the host-specificity the phage carried. In the DNA of P22 grown in strains harboring the modifying drug-resistance-transfer-factor N-3, the 5MeCyt content was at least twice that after growth in strains lacking the factor. In contrast, the 6MeAde level of P22 DNA was unaffected by the presence or absence of the factor. The 6MeAde and 5MeCyt levels were unaffected by factors 222 and N-1, which do not modify phage DNA. The 5MeCyt/6MeAde ratio was only slightly higher in the DNA of Salmonella strains that had received the N-3 factor. After transfer of the N-3 factor to Escherichia coli strain B, which normally lacks 5MeCyt, a high content of 5MeCyt is observed. We conclude that the N-3 factor controls a DNA methylase specific for cytosine residues. If the N-3 host specificity is imparted by cytosine methylation, this would be the first instance where a biological role for 5MeCyt has been elucidated.

Adenine↗