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A I Bukhari

Publications and source records attributed to A I Bukhari.

At least 37 records · Page 2Linked to original sources
PubMed1980

Association of Mu-containing plasmids with the Escherichia coli chromosome upon prophage induction.

To determine the structure of a prophage-containing plasmid during Mu transposition, we have monitored the physical state of pSC101[unk]Mucts after thermoinduction. We have also examined the fate of a mini Mu plasmid constructed in vitro by deleting 27 kilobases from the center of the Mu prophage in pSC101[unk]Mucts. At various times after prophage induction, DNA was extracted from Mu or mini Mu plasmid-containing strains and subjected to electrophoresis in low concentration agarose gels followed by transfer of the DNA to nitrocellulose paper. Separate hybridization with (32)P-labeled pSC101 and Mu DNA revealed the position of the plasmids and the replication of Mu DNA. At times after induction when Mu replication was clearly visible, Mu and mini Mu plasmids were found to migrate with Escherchia coli DNA. This Mu-specific association requires the phage coded A and B proteins. Electron microscopy has shown that some of the associated DNA is comprised of circular plasmid molecules which appear to be in contact with the chromosomal DNA. These structures may represent intermediates or end products of the replication-integration process. The finding that Mu and mini Mu plasmids do not give rise to any detectable excision products and apparently remain intact during Mu transposition supports our proposal that the predominant event after Mu induction is the replication of Mu DNA in situ to generate integrative intermediates.

Bacteriophage mu↗
PubMed1978

A mutant of Escherichia coli which accumulates large amounts of coproporphyrin.

A mutant of Escherichia coli which accumulates a large amount of coproporphyrin, presumably because of a block in heme biosynthesis, has been isolated after nitrosoguanidine mutagenesis. On rich media, the mutant forms colonies which give bright orange fluorescence when illuminated with ultraviolet light. The mutant appears to be similar to a Salmonella typhimurium mutant, deficient in uroporphyrinogen III cosynthase, described by Sasarman and Desrochers ((1976) J. Bacteriol. 128, 717--721). A striking property of the mutant is that coproporphyrin is retained within the cells in rich media but is almost totally excreted out of cells in minimal glucose medium.

Coproporphyrins↗
PubMed1978

Insertion of a transposon for chloramphenicol resistance into bacteriophage Mu.

We have isolated mutants of bacteriophage Mu carrying the X mutations caused by the insertion of cam (Tn9), a transposon for chloramphenicol resistance. The Mu X cam mutants were obtained by selecting for heat-resistant survivors of a Mucts62, P1cam dilysogen. Like the previously described X mutants, Mu X cam mutants are defective prophages which can be excised from the host DNA at a frequency of 10(-5) to 10(-7) per cell. Tn9 insertions in Mu X cam mutants are located within 5000 base pairs of the left end of Mu DNA in a region that controls early replication functions of Mu. There is one EcoRI cleavage site in Tn9. The Tn9 transposon itself can be excised precisely from the Mu X cam mutants to generate wild type Mu. In most Mu X cam mutants, precise excision of Tn9 occurs at a low frequency (10(-6) per cell), whereas in some, the frequency is higher (10(-4) per cell). Mu X cam prophages can replicate after induction with the help of wild type Mu. The lysates containing Mu X cam particles, however, fail to transduce chloramphenicol resistance at a high frequency; Mu X cam mutants apparently have a cis dominant defect in integration.

Chloramphenicol↗
PubMed1978

Analysis of transposable elements inserted in the genomes of bacteriophages Mu and P1.

We have examined the genomes of the temperate bacteriophages Mu and P1 and some of their insertion mutants for hybridization with the prokaryotic transposable elements IS1 and IS2. We used the DNA blotting-hybridization technique in which denatured DNA fragments are transferred to nitrocellulose paper directly from agarose gels and hybridized to 32P-labeled probe DNA. The 800 base pair insertion in an X mutant of Mu was found to hybridize with IS1. The chloramphenicol resistance transposon, Tn9, in Mu X cam mutants was found to be located at or close to the sites of IS1 insertion in X mutants; Tn9 also hybridized with IS1. The restriction endonuclease BalI cleaved IS1 once; it cleaved Tn9 in all Mu X cam mutants twice to release a fragment of about 1700 base pairs. These results support the conclusion that Tn9 contains one copy of IS1 at each end. In the P1cam isolate, from which Tn9 was transposed to Mu, BalI made a third cut in Tn9 giving rise to fragments of about 850 base pairs. The data further suggested that Tn9 is present in tandem copies in the P1cam isolate we examined. P1 itself was found to harbor IS1. The two P1 strains tested had a common fragment containing IS1; one strain had an additional copy of IS1. The IS1 element common to the P1 strains was shown to be the site of the Tn9 insertion in the P1cam isolate examined. No hybridization between IS2 and any of the Mu and P1 strains could be detected.

Chloramphenicol↗
PubMed1978

Heteroduplex electron microscopy of phage Mu mutants containing IS1 insertions and chloramphenicol resistance transposons.

We have examined by electron microscopy the DNA heteroduplexes of six bacteriophage Mu mutants, Mu X cam, generated by the insertion of the Tn9 transposon for chloramphenicol resistance. Tn9 was found to be 2.8 +/- 0.2 kilobases (kb) in length and to consist of a cam determinant flanked by two IS1 sequences arranged in a direct order. In two of the six Mu X cam mutants, the Tn9 insertion was at a fixed location, 3.9 kb from the left, or c, end. In the other four mutants, the position of the insertion varied, even though the lysogenic cultures induced were grown from single colonies. The insertion was located at either 3.3 kb, 3.9 kb, or, less frequently, at 4.4 kb from the left end of the DNA. Furthermore, at low frequencies, the insertions were found to be in an orientation opposite to what predominated in the preparation. Thus, Tn9 in the Mu X cam mutants examined could appear to undergo rapid rearrangements during Mu growth or over a few generations of cell growth. One of the Tn9 insertion sites was apparently the same as that for a 0.8 kb insertion found in a Mu X mutant. This latter insertion was identified as an IS1 sequence. The DNA molecules from all the Mu X cam mutant phage particles were found to be missing the bacterial DNA at the S (right) end, along with a variable amount of the adjoining Mu DNA in the beta region. This observation supports the headful packaging model for Mu DNA.

Chloramphenicol↗
PubMed1978

Bacteriophage Mu-induced modification of DNA is dependent upon a host function.

The DNA of bacteriophage Mu, extracted from induced lysates, is partially resistant to digestion by the endonuclease BalI. This modification of DNA is controlled by the Mu modification function (mom), which acts in conjunction with the dam (DNA-adenine methylation) function of Escherichia coli. Since the BalI recognition site is apparently different from the dam recognition site, these results imply that either the specificity of the dam function is changed by the mom function or the mom function requires the dam function for its activity.

Coliphages↗
PubMed1977

State of prophage Mu DNA upon induction.

We have compared the process of prophage lambda induction with that of prophage Mu. According to the Campbell model, rescue of lambda DNA from the host DNA involves reversal of lambda integration such that the prophage DNA is excised from the host chromosome. We have monitored this event by locating the prophage DNA with a technique in which DNA of the lysogenic cells is cleaved with a restriction endonuclease and fractionated in agarose gels. The DNA fragments are denatured in gels, transferred to a nitrocellulose paper, and hybridized with 32P-labeled mature phage DNA. The fragments containing prophage DNA become visible after autoradiography. Upon prophage lambda induction, the phage-host junction fragments disappear and the fragment containing the lambda att site appears. No such excision is seen in prophage Mu. The Mu-host junction fragments remain intact well into the lytic cycle, when Mu DNA has undergone many rounds of replication and apparently many copies of Mu DNA have been integrated into the host DNA. Therefore, we postulate that Mu DNA replicates in situ and the replication generates a form of Mu DNA active in the integrative recombination between Mu DNA and host DNA. This type of mechanism may be common to many transposable elements.

Coliphages↗
PubMed1976

Genetic analysis of heterogeneous DNA circles formed after prophage Mu induction.

Induction of a Mu prophage in Escherichia coli Hfr strains lyosgenic for Mu cts62 leads to the generation of F' episomes. Each episome thus formed carries at least one copy of the Mu genome. These results suggest that integration of Mu is mandatory for the formation of the heterogeneous circles during the lytic cycle. The circles may be precursors for phage maturation.

Coliphages↗