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H Hamza

Publications and source records attributed to H Hamza.

At least 37 records · Page 2Linked to original sources
PubMed1988

Reciprocal exchanges instigated by large heterologies in the b2 gene of ascobolus are not associated with long adjacent hybrid DNA stretches.

In the gene b2 of Ascobolus immersus, large heterologies increase the frequencies of reciprocal exchanges on their upstream border (corresponding to the high non-Mendelian segregation side). Tests were made to determine whether these reciprocal exchanges, instigated by large heterologies, resulted from the blockage of a Holliday junction bordering a hybrid DNA tract extending from the end of the gene to the heterology. Three types of experiments were performed to answer this question. In all cases, results did not correlate the presence of reciprocal exchanges instigated by large heterologies with the presence of adjacent hybrid DNA tracts. These reciprocal exchanges were rarely associated with postmeiotic segregation at upstream markers, they were not associated with gene conversion of a marker within the interval and their frequency was not decreased by decreasing the frequency of hybrid DNA formation in the gene. These results led to the proposal of the existence of a precursor to reciprocal exchange different from a single branch-migrating Holliday junction. This precursor migrates rightward and its migration is dependent on the DNA sequence homology. The existence of this precursor does not exclude that reciprocal exchanges resulting from the maturation of single Holliday junctions bordering adjacent hybrid DNA tracts could also occur.

Ascomycota↗
PubMed1987

[Unusual aspects of the late manifestations of diaphragmatic hernia].

A 5-year-old boy investigated for abnormality in right cardiophrenic angle was found on radiologic and perioperative exploration to have a large diaphragmatic hernia allowing right intrathoracic passage of stomach and colon. The diaphragmatic defect included a wide left middle diaphragmatic Bochdalek cleft adherent to hiatal orifice due to agenesis of pillars.

Child, Preschool↗
PubMed1986

Two mechanisms for directional gene conversion.

G234 is a large silent deletion located in the middle of gene b2, which controls spore pigmentation in Ascobolus immersus. Its gene conversion directionality was studied in asci, which show evidence of heteroduplex DNA at flanking markers, and was compared to the behavior of closely linked single-base-pair insertions or deletions. We found that with the G234 deletion, the genotype of the donor strand in the heteroduplex is preferentially recovered, irrespective of its G234 or wild-type nature, whereas with single-base-pair insertions or deletions, the direction of conversion favors one genotype, whether it was the donor or the recipient strand. We conclude that there exists two mechanisms for directional gene conversion, the "donor-directed" conversion mechanism being epistatic to the "genotype-directed" one. We discuss these data with regard to models for mismatch repair.

Ascomycota↗
PubMed1981

Hybrid DNA formation during meiotic recombination.

G234 is a silent mutation located in the middle of gene b2, which controls spore pigmentation in Ascobolus immersus. Its effect on the aberrant segregation patterns of while spore mutants located in the same gene was investigated. When heterozygous, G234 decreases the frequency of aberrant segregations of the mutants located on its right, toward the low conversion end. It almost completely suppresses the aberrant 4:4 asci for mutants giving postmeiotic segregation and decreases the disparity between the 6 wild-type:2 mutant and 2 wild-type:6 mutant aberrant asci for mutants giving only these types of convertant asci. These effects are polar; G234 does not change the aberrant segregation pattern of the mutants located on its left, toward the high conversion end. This behavior suggests that G234 blocks the migration of the symmetric phase of hybrid DNA that diffuses from the high conversion end but does not prevent the formation of asymmetrical hybrid DNA. Taking into account previous observations, we conclude that the high conversion end corresponds to a region of asymmetric initiation of recombination rather than to a region of preferential ending of recombination. The asymmetric hybrid DNA first formed is further changed into a symmetric phase that extends via branch migration toward the low conversion end.

DNA, Fungal↗
PubMed1981

[Glomerulosclerosis: myeloma or diabetes? (author's transl)].

A 52 year old man was admitted to hospital for persistent back pain, fixed proteinuria of 6g/24 h that lead to the nephrotic syndrome (proteids 40 g/l, albumin 21,2 g/l). Two possible etiologies were envisaged: 1) Myeloma with K light chains as evidenced by biological findings (absence of normal Ig, presence of K light chains both in blood and urine, malignant medullary plasmocytosis) as well as x-rays (small punched out lesions). 2. Diabetes mellitus (blood glucose 2,4 g/l) with retinal and neurological involvement. Percutaneous renal biopsy revealed nodular glomerular sclerosis compatible with both diabetes and myeloma as well as homogeneous refringent thickening of tubular basement membranes more specific of myloma. No amyloid deposits, myelomatous casts were seen and anti-K light chain fixation was negative at immunofluorescence. An evolution of 33 months duration let to chronic renal failure (plasma creatinine 47 mg/l). The respective role of myeloma and diabetes in the genesis of this glomerular nephropathy are discussed.

Biopsy↗