Genetic and biochemical properties of revertants at the rudimentary locus in Drosophila melanogaster

Human enhancer of rudimentary is a molecular partner of PDIP46/SKAR, a protein interacting with DNA polymerase delta and S6K1 and regulating cell growth

Enhancer of rudimentary (ER) is a small protein that has a unique amino acid sequence and structure. Its highly conserved gene has been found in all eukaryotic kingdoms with the exception of fungi. ER was proposed to be involved in the metabolism of pyrimidines and was reported to act as a transcriptional repressor in a cell type-specific manner. To further elucidate ER functions, we performed the yeast two-hybrid screen of the human lung cDNA library for clones encoding proteins interacting with the human ER protein. The screen yielded polymerase delta interacting protein 46 or S6K1 Aly/REF-like target (PDIP46/SKAR), a protein possessing one RNA recognition motif (RRM) and being a protein partner of both the p50 subunit of DNA polymerase delta and p70 ribosomal protein S6 kinase 1 (S6K1). This interaction was further confirmed in vitro by the glutathione S-transferase-ER pull-down of a protein of 46 kDa from a nuclear extract from human cells which was identified as PDIP46/SKAR by tandem mass spectrometry. The bipartite region of PDIP46/SKAR interacting with ER comprising residues 274-421 encompasses the docking site for S6K1 within the RRM and two serines phosphorylated by S6K1. ER and both isoforms of PDIP46/SKAR share the same nuclear localization in the mammalian cells and their genes display a ubiquitous pattern of expression in a variety of human tissues, so the interaction between ER and PDIP46/SKAR has an opportunity to occur universally in mammalian cells. Because PDIP46/SKAR is involved in the regulation of cell growth its interaction with ER may suggest some function for ER in that control.

Modifier of rudimentary p1, mod(r)p1, a trans-acting regulatory mutation of rudimentary

Modifier of rudimentaryp1 (mod(r)p1) is a hybrid dysgenesis-induced mutation isolated as a suppressor of rhd1, a hypomorphic rudimentary(r) allele in Drosophila melanogaster.mod(r)p1 has opposite effects on two of the rudimentary mutant phenotypes. It suppresses the wing truncation associated with hypomorphic r alleles, which was the phenotype used to isolate it. On the other hand, it does not suppress the sterility of r females and in fact decreases the fertility of wild-type females. This infertility is associated with a drastic decrease in r expression in mod(r)p1 females. P elementagging was used to clone the mutant allele, mod(r)p1. Subsequently, 28 kb of genomic DNA encompassing the wild-type mod(r) gene in the chromosomal region 1B was cloned. mod(r) encodes a 1.3 kb transcript which is not detected in the mod(r)p1 mutant. The sequences of mod(r) cDNA clones reveal that the gene encodes a protein of 200 amino acids in length. When compared to sequences in GenBank, the amino acid sequence did not reveal any long sequences similarities. However, the structure of the protein reveals similarities to known transcription factors. The N-terminal half of the protein is very acidic, whereas the C-terminal half is basic. The basic domain suggests a possible DNA-binding domain, while the acidic domain suggests a transcriptional activation domain. Consistent with this possibility is the fact that mod(r) acts through the 5' control region of the rudimentary gene to control its expression.

Two non-gypsy rudimentary mutations and their suppression by mutations of suppressor of Hairy-wing in Drosophila

Two spontaneous mutations of rudimentary, the gene encoding the first steps of de novo pyrimidine biosynthesis in Drosophila, are suppressed by mutant alleles of the suppressor of Hairy-wing locus. This interaction differs from typical su(Hw) suppression in that neither rudimentary allele is associated with an insertion of the gypsy retrotransposon. One allele, rsP1, appears to be a point mutation. Adult rsP1 homozygous females accumulate substantially less 7.3 kb rudimentary transcript than do wild-type females. The other allele, rsP2, is an insertion of an mdg3 retrotransposon in the sixth exon of rudimentary and in the opposite transcriptional orientation. This insertion divides the rudimentary locus into two separate, yet functional, transcription units by truncating transcription from the rudimentary promoter and promoting transcription of downstream rudimentary sequences. Phenotypic suppression of both rsP1 and rsP2 by mutant alleles of the suppressor of Hairy-wing locus correlates with enhanced levels of the rsP1 and rsP2 transcripts.

P-element-induced control mutations at the r gene of Drosophila melanogaster

The P-M hybrid dysgenesis system was used to produce five putative regulatory mutations at the rudimentary locus, r. All five mutations were the result of insertions at the 5' end of the gene, upstream of the proposed start of transcription. All of the mutants displayed a leaky wing phenotype, and four of the mutants showed an uncoupling of the wing and female-sterility phenotypes, suggesting that they altered the normal spatial and temporal expression of the r gene. Four of the insertions were P elements. The fifth insertion, which was larger than an intact P element, consisted of a small P element connected to non-P-element DNA. Two of the mutants produced very little r transcript in adult females and were clustered 80 to 150 base pairs upstream of the start of transcription. The other three mutants had higher levels of r transcript in adult females and were clustered 440 to 500 base pairs upstream of the start of transcription. All of the data suggest that the insertions are in a 5' noncoding region of the r gene involved in the control of its spatial and temporal expression.

P-element-induced control mutations at the r gene of Drosophila melanogaster

The P-M hybrid dysgenesis system was used to produce five putative regulatory mutations at the rudimentary locus, r. All five mutations were the result of insertions at the 5' end of the gene, upstream of the proposed start of transcription. All of the mutants displayed a leaky wing phenotype, and four of the mutants showed an uncoupling of the wing and female-sterility phenotypes, suggesting that they altered the normal spatial and temporal expression of the r gene. Four of the insertions were P elements. The fifth insertion, which was larger than an intact P element, consisted of a small P element connected to non-P-element DNA. Two of the mutants produced very little r transcript in adult females and were clustered 80 to 150 base pairs upstream of the start of transcription. The other three mutants had higher levels of r transcript in adult females and were clustered 440 to 500 base pairs upstream of the start of transcription. All of the data suggest that the insertions are in a 5' noncoding region of the r gene involved in the control of its spatial and temporal expression.