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J L Rossignol

Publications and source records attributed to J L Rossignol.

35 records · Page 2Linked to original sources
PubMed1988

Synthesis and receptor binding of polynuclear organometallic estradiol derivatives.

Twelve novel organometallic derivatives of estradiol were synthesized with the aim of utilizing organometallic cold bioprobes as radioisotopic labels substitutes for steroid hormone receptor assays. For this purpose, we envisaged the attachment of several stable cobalt, molybdenum, osmium carbonyl clusters (tetra- and pentanuclear species) at estradiol 17 alpha-, 16 alpha-, 2- or 4-positions. The binding affinity of these new complexes for uterine estradiol receptor has been measured by the competitive binding method. The results show that the 17 alpha-position can tolerate substitution by bulky organometallic groups (especially in the case of cobalt and molybdenum carbonyl clusters). Estradiol derivatives which are functionalized at C-4 and C-16 alpha bind estradiol receptor with reasonable affinity and the RBA values are the same for the complexed and uncomplexed hormones. The 2- position is more sensitive to organometallic substitution and the complexation at the 2- alkyne results in a dramatic decrease of the RBA values. These results show that the attachment of polynuclear moieties in estradiol 17 alpha-, 4- and 16 alpha-, positions gives rise to compounds which are of potential utility in a new non-radioisotopic receptor assay since the metal-carbonyl markers are readily detected by high-sensitivity Fourier-transform infra-red spectroscopy.

Animals↗
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↗
PubMed1988

Hybrid DNA extension and reciprocal exchanges: alternative issues of an early intermediate during meiotic recombination?

Large heterologies in gene b2 strongly increase the frequencies of reciprocal exchanges on their left border, towards the high conversion end. In a previous study, we observed that heterozygous point mutations located in the high conversion end (region F) stimulate the reciprocal exchanges instigated by the large heterology 138. We have defined some properties of this stimulation. The effect does not depend on the nature of the large heterology used. It is effective only with point mutations located on the left side of the large heterology. It does not depend on the number of heterozygosities accumulated in region F. It is not specific on the location of point mutations in region F: it decreases from region F (left end) to region E (middle part of b2). It is correlated with the mismatch correction efficiencies of the point mutations used. It is not observed in the absence of a large heterology. Point mutation heterozygosities which stimulate reciprocal exchanges also decrease the frequency of HDNA formation in gene b2. We propose a model in which reciprocal exchanges on the one hand and hybrid DNA formation on the other hand correspond to alternative processings of a common recombination intermediate.

Ascomycota↗
PubMed1986

The MET2 gene of Saccharomyces cerevisiae: molecular cloning and nucleotide sequence.

A 5.1-kb DNA fragment from Saccharomyces cerevisiae, which complements a yeast met2 mutant strain, has been cloned. This fragment contains the wild-type MET2 gene which codes for the homoserine O-transacetylase, one of the methionine biosynthetic enzymes. The presence of the MET2 gene has been shown by integrative transformation experiments and genetic analyses of the resulting transformants. The complete nucleotide sequence of a 2826-bp DNA fragment carrying the MET2 gene has been determined. The sequence contains one major open reading frame of 438 codons, giving a calculated Mr of 48,370 for the encoded protein. We have identified the transcriptional product of the MET2 gene and estimated its size at 1650 nucleotides.

Acetyltransferases↗
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↗
PubMed1983

Gene conversion: point-mutation heterozygosities lower heteroduplex formation.

The effects of heterozygosity on meiotic gene conversion characteristics have been studied in the fungus Ascobolus immersus. The non-Mendelian segregation patterns of seven white ascospore mutants of the b2 gene were established in the presence or the absence of additional neighbouring allelic mutations. These correspond to nine different double mutants with wild-type or pseudo-wild-type phenotypes, constituted by two +1, -1 frameshift mutations of complementary phases. When heterozygous, these double point mutations decrease, by an average of one third, the gene conversion frequencies of the mutants located on their right, toward the low conversion end of the gene. The decrease corresponds either to a reduction in all classes of non-Mendelian segregation (6:2, 5:3 and aberrant 4:4 asci) or to a reduction restricted to the single class of aberrant 4:4 asci. These modifications are explained by changes in hybrid DNA parameter values: frequencies of formation and modalities of distribution (asymmetric versus symmetric ratio). Besides the nature of the non-homology, point mutation versus deletion, which leads to quantitative differential effects, the region where the non-homology is located within the gene also appears to play an important role.

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↗
PubMed1979

Disparity of gene conversion in frameshift mutants located in locus b2 of Ascobolus immersus.

The frequency of conversion and the disparity in the direction of conversion were studied for six frameshift mutants lying in locus b2 of Ascobolus immersus and giving more 2 wild type:6 mutant (2+6m) than 6 wild type:2 mutant (6+2m) aberrant asci (type B). The frequency of conversion decreased from left to right in the locus. The disparity steadily increased from left to right and then reached a plateau. Twenty-two frameshift mutants giving more 6+2m than 2+6m aberrant asci (type A) and closely linked to three type B mutants were also studied; they showed the same frequency of conversion and the same disparity (but in the opposite direction) as the type B mutant to which they are linked. The polar variation of both the frequency of conversion and the disparity as a function of position were expected on the basis of a previous study of 15 mutants giving postmeiotic segregations and located in locus b2. This variation is assumed to reflect the existence of a preferential region for the initiation of hybrid DNA (HDNA) during recombination and a duality in the distribution of this HDNA, with preponderant asymmetrical HDNA near the starting point and preponderant symmetrical HDNA farther from it.

Journal Article↗
PubMed1976

[High frequency reversion of a spontaneous mutant in Ascobolus immersus].

A spontaneous spore-colour mutation located in the gene b2 of A. immersus gives a high frequency of reversion. 8 distinct revertant phenotypes have been defined. The mutations corresponding to these revertants are located at the same site or very near the original mutation. The hypothesis that the mutation by itself is responsable for the observed reversions is advanced.

Ascomycota↗
PubMed1974

The suppression of gene conversion and intragenic crossing over in Ascobolus immersus: evidence for modifiers acting in the heterozygous state.

Four distinct systems cv1, cv2, cv4 and cv6 behaving as monogenic factors have been found in the stock 28 of Ascobolus immersus. They each specifically suppress gene conversion in a spore pigmentation gene (respectively, b1, b2, b4 and b6). In the gene b2, where this phenomenon was studied in most detail, the effect of cv2 on the suppression of gene conversion is almost total; intragenic recombination is very strongly diminished and crossing over is also affected. In the genes b1, b2 and b4 the suppression of conversion is observed only when the corresponding modifier (cv1, cv2 and cv4) is in the heterozygous condition. It is likely that cv6 acts in the same way on b6. cv1 and b1 on one hand, cv2 and b2 on the other, are very closely linked; no recombination was observed between these modifiers and the corresponding spore pigmentation genes. The same genetic distance is observed between the linked genes b4 and b6 and between cv4 and cv6. This could indicate that these two modifiers are also closely linked to the corresponding genes. A possible effect of cv4 on intergenic recombination between b4 and b6 was shown: here again it acts by diminishing the frequency of recombination when cv4 is in the heterozygous state. The problem of the nature of the cv modifiers is discussed.

Ascomycota↗