Expression and properties of wild-type and mutant forms of the Drosophila sex comb on midleg (SCM) repressor protein.
The Sex comb on midleg (Scm) gene encodes a transcriptional repressor of the Polycomb group (PcG). Here we show that SCM protein is nuclear and that its expression is widespread during fly development. SCM protein contains a C-terminal domain, termed the SPM domain, which mediates protein-protein interactions. The biochemical function of another domain consisting of two 100-amino-acid-long repeats, termed "mbt" repeats, is unknown. We have determined the molecular lesions of nine Scm mutant alleles, which identify functional requirements for specific domains. The Scm alleles were tested for genetic interactions with mutations in other PcG genes. Intriguingly, three hypomorphic Scm mutations, which map within an mbt repeat, interact with PcG mutations more strongly than do Scm null alleles. The strongest interactions produce partial synthetic lethality that affects doubly heterozygous females more severely than males. We show that mbt repeat alleles produce stable SCM proteins that associate with normal sites in polytene chromosomes. We also analyzed progeny from Scm mutant germline clones to compare the effects of an mbt repeat mutation during embryonic vs. pupal development. We suggest that the mbt repeat alleles produce altered SCM proteins that incorporate into and impair function of PcG protein complexes.
Department of Biochemistry and Department of Genetics and Cell Biology, University of Minnesota, St. Paul, Minnesota 55108, USA.
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Bornemann
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Miller
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Simon
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D002467:Cell Nucleus / Q000737:chemistry; D002875:Chromosomes / Q000737:chemistry; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics* / Q000254:growth & development; D005260:Female; D015870:Gene Expression; D017344:Genes, Insect / Q000235:genetics; D005804:Genes, Lethal / Q000235:genetics; D019476:Insect Proteins / Q000032:analysis / Q000235:genetics; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D009687:Nuclear Proteins; D009928:Organ Specificity; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D020449:Repetitive Sequences, Amino Acid; D012097:Repressor Proteins / Q000032:analysis / Q000235:genetics*; D015183:Restriction Mapping; D014157:Transcription Factors
D000906:Antibodies; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D019476:Insect Proteins; D009687:Nuclear Proteins; C066770:Pc protein, Drosophila; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; C099357:SCM protein, Drosophila; D014157:Transcription Factors; C060849:z protein, Drosophila; C066591:abd-A protein, Drosophila; D063150:Polycomb Repressive Complex 1