Mechanism of suppression in Drosophila: evidence for a macromolecule produced by the su(s)+ locus that inhibits sepiapterin synthase

Genetic analysis of the X-chromosomal region 1E-2A of Drosophila melanogaster

Reversion mutagenesis of three single P elements located in the cytogenetic interval 1E-2A at the tip of the X chromosome of Drosophila melanogaster was used to recover new deletions in this chromosomal region. The deletions obtained include small aberrations within region 2A and larger lesions extending from 2A into 1E and 1B. All three screens also yielded terminal deficiencies. The new deficiencies, together with previously characterized rearrangements, were analyzed for their complementation behaviour with the maternal effect locus fs(1) Nasrat and lethal loci in the region. These analyses provide an overall genetic map of the interval 1E-2A. In addition, the smaller deletions were physically mapped within cloned genomic DNA of the 2A region.

The Drosophila suppressor of sable gene encodes a polypeptide with regions similar to those of RNA-binding proteins

The nucleotide sequence of the Drosophila melanogaster suppressor of sable [su(s)] gene has been determined. Comparison of genomic and cDNA sequences indicates that an approximately 7,860-nucleotide primary transcript is processed into an approximately 5-kb message, expressed during all stages of the life cycle, that contains an open reading frame capable of encoding a 1,322-amino-acid protein of approximately 150 kDa. The putative protein contains an RNA recognition motif-like region and a highly charged arginine-, lysine-, serine-, aspartic or glutamic acid-rich region that is similar to a region contained in several RNA-processing proteins. In vitro translation of in vitro-transcribed RNA from a complete cDNA yields a product whose size agrees with the size predicted by the open reading frame. Antisera against su(s) fusion proteins recognize the in vitro-translated protein and detect a protein of identical size in the nuclear fractions from tissue culture cells and embryos. The protein is also present in smaller amounts in cytoplasmic fractions of embryos. That the su(s) protein has regions similar in structure to RNA-processing protein is consistent with its known role in affecting the transcript levels of those alleles that it suppresses.

The Drosophila suppressor of sable gene encodes a polypeptide with regions similar to those of RNA-binding proteins

The nucleotide sequence of the Drosophila melanogaster suppressor of sable [su(s)] gene has been determined. Comparison of genomic and cDNA sequences indicates that an approximately 7,860-nucleotide primary transcript is processed into an approximately 5-kb message, expressed during all stages of the life cycle, that contains an open reading frame capable of encoding a 1,322-amino-acid protein of approximately 150 kDa. The putative protein contains an RNA recognition motif-like region and a highly charged arginine-, lysine-, serine-, aspartic or glutamic acid-rich region that is similar to a region contained in several RNA-processing proteins. In vitro translation of in vitro-transcribed RNA from a complete cDNA yields a product whose size agrees with the size predicted by the open reading frame. Antisera against su(s) fusion proteins recognize the in vitro-translated protein and detect a protein of identical size in the nuclear fractions from tissue culture cells and embryos. The protein is also present in smaller amounts in cytoplasmic fractions of embryos. That the su(s) protein has regions similar in structure to RNA-processing protein is consistent with its known role in affecting the transcript levels of those alleles that it suppresses.

Purification and characterization of 6-pyruvoyl-tetrahydropterin synthase from Drosophila melanogaster

The enzyme 6-pyruvoyl-tetrahydropterin synthase (PTP synthase), which catalyzes the conversion of 7,8-dihydroneopterin triphosphate to 6-pyruvoyl tetrahydropterin, has been purified approx. 230-fold to apparent homogeneity from head extracts of Drosophila melanogaster. A partially purified 6-pyruvoyl-tetrahydropterin reductase (PTP reductase) was also prepared and in its presence, along with Mg2+ and NADPH, the purified PTP synthase converted 7,8-dihydroneopterin triphosphate to metastable 6-lactoyltetrahydropterin, which was autoxidized to sepiapterin under aerobic conditions. Purified PTP synthase had a specific activity of 3792 units per mg protein and migrated as a single protein band on both nondenaturing polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified active enzyme consisted of at least two identical subunits which had a molecular mass of 37.5 kDa on SDS-PAGE and NH2-Asx-Pro- as N-terminal amino acids. The native enzyme in crude extract was shown to be more complex, existing as higher multimeric forms.

Molecular study of the retrovirus-like transposable element 412, a 20-OH ecdysone responsive repetitive sequence in Drosophila cultured cells

Used at a physiological concentration, the steroid hormone 20-hydroxyecdysone (20-OHE) induces, in Kc cultured Drosophila melanogaster cells, important and specific changes. Modifications occur at morphological and enzymatical levels. Variations in specific protein synthesis are observed. At the molecular level, 20-OHE particularly induces a decrease in expression of the mobile dispersed genetic element 412. This repeated element which belongs to the "copia-like" family is more widely represented in Kc cells (80 fold) compared to fly cells (25 fold). 412 transcripts are heterogeneous in size, essentially polyadenylated and restricted to the nucleus. A minimal concentration of 10(-8) M and a time treatment of 16 hours are necessary to obtain a strong decrease in 412 expression. The decrease is at least an effect on these sequences at the transcriptional level. Structural similarities between the 412 element and the proviral forms of vertebrate retroviruses are strengthened by the characterization of extrachromosomal circular DNA forms revealed by the 412 probe. Quantifying experiments have shown that the steady state level of such forms is not affected by the steroid treatment.

Mechanism of suppression in Drosophila: regulation of tryptophan oxygenase by the su(s)+ allele

The suppressor gene, su(s)2, in Drosophila melanogaster restores the production of red and brown eye pigments for some purple and vermilion mutant alleles, respectively. We showed previously that the product of the su(s)+ allele caused inhibition of the sepiapterin synthase A produced by the purple mutant but did not affect the wild-type enzyme. Suppression was accomplished by removing su(s)+ from the genome. We now report that the tryptophan oxygenase, produced by suppressible vermilion alleles, is also inhibited by extracts from su(s)+ flies. The inhibition of the vermilion enzyme can be reduced or eliminated, respectively, by prior storage of the extract at 4 or -20 degrees C or by boiling, whereas the wild-type enzyme is not affected by extracts of su(s)+ flies. Also, when the suppressible vermilion strain is raised on certain diets, brown eye pigment production occurs. This epigenetic suppression was reduced by the presence of an extra copy of su(s)+ in the genome. These data support a posttranslational mechanism for regulation of enzyme activity in which the activity of the mutant enzyme is reduced by the product of the su(s)+ allele. How the su(s)+ gene product can distinguish between the normal and the mutant forms of these two enzymes is discussed, along with other mechanisms for suppression that are currently under investigation.

Molecular cloning of suppressor of sable, a Drosophila melanogaster transposon-mediated suppressor

A hybrid dysgenesis-induced allele [su(s)w20] associated with a P-element insertion was used to clone sequences from the su(s) region of Drosophila melanogaster by means of the transposon-tagging technique. Cloned sequences were used to probe restriction enzyme-digested DNAs from 22 other su(s) mutations. None of three X-ray-induced or six ethyl methanesulfonate-induced su(s) mutations possessed detectable variation. Seven spontaneous, four hybrid dysgenesis-induced, and two DNA transformation-induced mutations were associated with insertions within 2.0 kilobases (kb) of the su(s)w20 P-element insertion site. When the region of DNA that included the mutational insertions was used to probe poly(A)+ RNAs, a 5-kb message was detected in wild-type RNA that was present in greatly reduced amounts in two su(s) mutations. By using strand-specific probes, the direction of transcription of the 5-kb message was determined. The mutational insertions lie in DNA sequences near the 5' end of the 5-kb message. Three of the seven spontaneous su(s) mutations are associated with gypsy insertions, but they are not suppressible by su(Hw).

Molecular cloning of suppressor of sable, a Drosophila melanogaster transposon-mediated suppressor

A hybrid dysgenesis-induced allele [su(s)w20] associated with a P-element insertion was used to clone sequences from the su(s) region of Drosophila melanogaster by means of the transposon-tagging technique. Cloned sequences were used to probe restriction enzyme-digested DNAs from 22 other su(s) mutations. None of three X-ray-induced or six ethyl methanesulfonate-induced su(s) mutations possessed detectable variation. Seven spontaneous, four hybrid dysgenesis-induced, and two DNA transformation-induced mutations were associated with insertions within 2.0 kilobases (kb) of the su(s)w20 P-element insertion site. When the region of DNA that included the mutational insertions was used to probe poly(A)+ RNAs, a 5-kb message was detected in wild-type RNA that was present in greatly reduced amounts in two su(s) mutations. By using strand-specific probes, the direction of transcription of the 5-kb message was determined. The mutational insertions lie in DNA sequences near the 5' end of the 5-kb message. Three of the seven spontaneous su(s) mutations are associated with gypsy insertions, but they are not suppressible by su(Hw).

Molecular characterization of the Drosophila vermilion locus and its suppressible alleles

We have cloned vermilion (v), one of the genes required for brown eye pigment synthesis in Drosophila, using a mutant (vH2a) "tagged" with the transposon P factor. Mutations that disrupt v gene expression are clustered within approximately 2 kilobases of DNA. A 1.4-kilobase transcript, homologous to this same region, is present in v+ RNA but absent in RNA from several v mutants. The spontaneous v alleles that are suppressed by the suppressor of sable [su(s)] are apparently identical insertions of 412, a copia-like transposable element. Preliminary evidence suggests that su(s)-suppressible alleles at other loci may also be 412 insertions.

Excision of the DBA ecotropic provirus in dilute coat-color revertants of mice occurs by homologous recombination involving the viral LTRs

The dilute (d) coat color mutation of DBA/2J mice is closely associated with the site of integration of an ecotropic murine leukemia provirus. In five independent dilute revertants (d+) examined, reversion to wild-type coat-color correlated with the loss of most of the ecotropic proviral genome, indicating that virus integration caused the mutation. Molecular cloning and restriction enzyme analysis of the viral preintegration site as well as two independent dilute revertants, showed that exactly one long terminal repeat (LTR) remained in each revertant DNA, suggesting that virus excision occurred by homologous recombination involving the viral LTRs.

Drosophila melanogaster mutations suppressible by the suppressor of Hairy-wing are insertions of a 7.3-kilobase mobile element

Certain spontaneous mutations of Drosophila melanogaster are suppressed by su(Hw), the suppressor of Hairy-wing (3R-54.8). We find that mutations suppressible by su(Hw) result from insertions of a mobile element at the affected loci. The element, named gypsy, is approximately 7.3 kilobases long and includes 0.5-kilobase direct terminal repeats. It was first identified in DNA cloned from the bithorax chromosomal region of several Drosophila stocks carrying suppressible mutations of the bithorax complex. Cloned gypsy DNA was used as a probe to test for the association of gypsy with suppressible mutations at various other loci by hybridization in situ. Gypsy was found to be associated with 19 suppressible alleles at 10 different loci: yellow, Hairy-wing, scute, diminutive, cut, lozenge, forked, Beadex, hairy, and the bithorax complex. It was found with wild-type or nonsuppressible mutations at any of these loci. Gypsy DNA was also used as a probe to clone the element and adjacent unique DNA from the loci of some suppressible mutations. This confirmed the presence of the full-length element and also provided cloned DNA from the previously uncloned loci scute and cut. The suppressor of Hairy-wing is generally recessive and behaves as a null mutation. Thus, the disruption of normal gene function caused by the inserted gypsy element appears to require some product of the wild-type suppressor gene, su(Hw)+.