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V Murray

Publications and source records attributed to V Murray.

At least 109 records · Page 6Linked to original sources
PubMed1987

Transversion-specific purine analogue mutagens and the mechanism of hydroxylaminopurine mutagenesis.

The tryptophan synthetase gene A series of mutants in E. coli has been used to examine the mutational specificity of over 80 purine base analogues. 4 purine analogues have been discovered that solely cause transversions. Evidence is presented that hydroxylaminopurine mutagenesis is caused by a covalent reaction of these compounds with DNA. The transversion-causing purine analogues are derivatives of 2-aminopurine (2AP) and 2,6-diaminopurine (2,6DAP). They stimulate the full reversion frequency of those trp A which can revert through an AT----CG transversion. 8 purine base analogues have been found that induce the AT----CG transversion at the trp A88 site; and 2-amino-6-methylaminopurine (2A6MAP) stimulates by 124-fold, 2-amino-6-ethylaminopurine by 20-fold, 2-methylaminopurine (2MAP) by 9.4-fold, 2,6-bismethylaminopurine by 25-fold, 2AP by 230-fold, 2,6DAP by 15-fold, 2.6-diaminopurine riboside by 5-fold, and 2-hydroxylaminopurine by 11-fold. The last 4 analogues also cause transitions. 2A6MAP, 2-amino-6-ethylaminopurine and 2,6-bismethylaminopurine stimulate only the AT----CG transversion while 2MAP additionally gives rise to AT----TA transversions. By testing other negative 2AP derivatives, the structural requirements necessary for AT----CG transversion mutagenesis have been determined. All 12 hydroxylaminopurine base analogues tested, 2,6-dimethoxyaminopurine and 2-hydrazinopurine were found to cause transition mutations. All of the compounds stimulated the AT----GC transition (by up to 1000-fold) and 11 of the 14 base analogues raised the GT----AT transition (by up to 450-fold). On increasing the hydroxylaminopurine concentration, the mutation frequency also increased concomitantly. Since 6-hydroxylamino-9-methylpurine and 6-methylhydroxylaminopurine cause transitions, the mechanism of hydroxylaminopurine mutagenesis cannot be entirely due to an alteration in tautomeric equilibria or "wobble" type base mispairing. It is proposed that a major mechanism for hydroxylaminopurine mutagenesis is due to the reaction of these compounds with the O6-position of guanine and the O4-position of thymine.

Adenine↗
PubMed1987

5-Amino-4-imidazolecarboxamide is a mutagen in E. coli.

5-Amino-4-imidazolecarboxamide (5A4IC), the base moiety of a common intermediate in de novo purine biosynthesis, was found to be mutagenic in E. coli. Using a series of mutants in the tryptophan synthetase A gene, 5A4IC was observed to cause transition and transversion mutations at similar levels. At 400 micrograms/ml in the growth medium, it stimulates the base substitution GC----AT 4.8-fold; AT----GC 20-fold; AT----CG (2 sites) an average of 6.0-fold; AT----TA 7.8-fold; and GC----CG 6.1-fold. The transversion GC----TA was not tested. In contrast to the base, 5-amino-4-imidazolecarboxamide riboside is not mutagenic at a similar molar concentration.

Aminoimidazole Carboxamide↗
PubMed1987

Nucleotide sequences of human alpha-DNA repeats.

We have sequenced eight cloned copies of the 340-bp EcoRI repeat of human alpha-DNA (alpha RI-DNA). Compared to the 'consensus' alpha RI-DNA sequence [Wu and Manuelidis, J. Mol. Biol., 142 (1980) 363-386], the eight clones had changes in 1.5, 2.1, 3.2, 3.2, 10.3, 12.9, 15.0 and 18.9% of base pairs. Jorgensen et al. [J. Mol. Biol., 187 (1986) 185-196] have described 21 sub-families of human alpha RI-DNA based on common base substitutions. Three of our sequences appear to be members of the sub-families described by Jorgensen et al., while the other five sequences are from previously undescribed sub-families.

Base Sequence↗
PubMed1985

The sequence specificity of bleomycin-induced DNA damage in intact cells.

Bleomycin causes lesions to DNA in intact cells and in purified DNA under appropriate conditions. Using a middle repetitive DNA sequence called alpha-DNA as a target sequence, we have compared the sequence specificity of bleomycin-induced DNA cleavage in intact human cells and in purified human DNA. Bleomycin induces numerous cleavage sites in alpha-DNA which vary widely in intensity and give rise to a complex pattern of bands on a DNA sequencing gel. Unexpectedly, the intensity and position of bleomycin-induced DNA cleavage sites are very similar in intact human cells and in purified human DNA.

Base Sequence↗
PubMed1985

Comparison of the sequence specificity of bleomycin cleavage in two slightly different DNA sequences.

The sequence specificity of bleomycin damage was investigated utilising 340 bp alpha-DNA (a middle repetitive sequence in the human genome) as a target sequence. The following significant facts were found:- i) The dinucleotides GT and GC were cleaved on all occasions, GA most of the time, and AT, AC, GG and AA cleaved some of the time; ii) The base immediately 5' to the purine-pyrimidine dinucleotides was found to be statistically highly significant in determining the degree of damage caused by bleomycin, while other nearest neighbour bases had no significant effect; iii) The sequence specificity of bleomycin damage was determined on both strands and it was found that damage on either strand follows the above dinucleotide preference and is independent of the extent of damage on the opposite strand; iv) Bleomycin damage was compared between genomic 340 bp alpha-DNA and a cloned alpha-DNA with eleven base substitutions relative to the "consensus" sequence. There were forty-nine detectable differences in intensity of damage between these two DNA molecules. Although four of the differences can be directly attributed to changes in base sequence, the remaining differences were not at the base substitution sites. Some of the differences were over fifty base pairs from the nearest base substitution. We propose that the majority of these differences are due to microvariation in the structure of DNA with a slightly different DNA sequence.

Base Sequence↗
PubMed1984

Diagnostic errors discovered by CT in patients with suspected stroke.

We assessed the frequency of stroke diagnostic errors revealed by CT in 197 patients. In five patients, CT was an emergency procedure. In the other 192 patients, CT was used to check diagnosis based on routine investigations. All but eight diagnoses (4%) were thereby confirmed. Either hemorrhage was discovered where an ischemic lesion had been suspected (2 cases) or the reverse (3 cases). Disorders other than stroke were found in three patients--subdural hematoma, hydrocephalus, and suspected tumor. Thus, few but important errors were revealed by the CT investigations.

Adult↗
PubMed1983

The diagnostic accuracy of CSF analyses in stroke.

The ability of routine analyses of cerebrospinal fluid (CSF) to differentiate between haemorrhage and infarction was evaluated in 231 stroke patients, whose diagnoses were based on computed tomography or autopsy. In all diagnostic groups the mean protein level was above normal, the highest values being associated with haemorrhage. Taking a protein level greater than 1 g/l to be characteristic of bleeding, sensitivity was 89% and specificity 92%. Spectrophotometric CSF absorbance was measured at wave lengths of 410, 415, 455 and 630 nm. Validity was equal for the first three. Taking absorbance greater than or equal to 0.040 at 415 nm to be diagnostic for haemorrhage, sensitivity was 72% and specificity 94%. The human eye was almost as sensitive as spectrophotometry in this context. Thus, among 100 patients with stroke, 7-9 out of 10 plausible cases of haemorrhage would be identified by means of routine CSF analyses. At the same time, 5-9 patients with ischaemic lesions would be diagnosed incorrectly as bleedings.

Blood Cell Count↗
PubMed1981

Properties of DNA polymerases from young and ageing human fibroblasts.

A comparison was made between two methods of isolating DNA polymerases from MRC-5 fibroblasts. The first method produces DNA polymerase-alpha with a lower molecular weight and other properties that are not normally found for this enzyme. It was concluded that this method produces proteolytically degraded DNA polymerase-alpha. A second method was developed which produces DNA polymerase-alpha with all the normal properties of this enzyme. The specific activity of DNA polymerase was reduced in senescent MRC-5 fibroblasts approximately 2--4-fold. DNA polymerase-alpha accounts for 95% of polymerase activity in young cells and its specific activity during the fibroblast lifespan correlates with the declining cellular growth rate. DNA polymerase-beta is present at 0.3-3% of total cellular activity and its specific activity does not correlate with cellular growth rate. DNA polymerase-gamma accounts for 5% of the polymerase activity in young cells and 20% in old cells. However, the specific activity of the polymerase-gamma is constant throughout the lifespan of MRC-5. The 5 S DNA polymerase-alpha has an increased in vitro error frequency (average 3.6) compared to the 7 S polymerase-alpha. In addition the proportion of 5 S polymerase-alpha rises from 7% in young cells to 29% in senescent cells in an apparently exponential fashion.

Aging↗
PubMed1980

A study of stroke patients treated in a non-intensive stroke unit or in general medical wards.

To study the representativity and outcome of patients admitted to a stroke unit (SU) (n = 269), a comparison was made with all stroke patients treated in general medical wards (GMW) (n = 225) in the same hospital during two years. There was no difference between the patient groups regarding sex, age, previous cardiovascular diseases or neurological deficit on admission. As expected, more diagnostic examinations were performed in the SU than in the GMW where a diagnosis of ill-defined stroke was very frequent. A higher frequency of lumbar puncture with CSF spectrophotometry would have increased considerably the number of specific diagnoses in the GMW. Acute and, particularly, secondary prophylactic treatment was more often given in the SU. There was no difference between the patient groups regarding mortality or length of hospital stay.

Aged↗