The extra sex combs (esc) gene product is a transcriptional repressor of homeotic genes. Although it is classified in the Polycomb group (PcG) on the basis of phenotypic criteria, it is distinct from most other PcG repressors in its time of action during development. We describe the temporal profile of esc mRNA expression during embryogenesis and the stage-specific rescue of esc mutants with a heat shock-inducible esc cDNA transformation construct. Both experiments support the idea that esc product plays an early, transient role in repression of homeotic genes. We also present the sequence of a full-length esc cDNA. The predicted esc protein is composed primarily of multiple copies of a repeat motif, termed the WD40 repeat, which are likely used in protein-protein contact. We provide evidence that individual copies of the esc WD40 repeats are needed for function in vivo. We suggest that esc protein is an adaptor that binds to multiple protein partners and assists in the assembly or targeting of other PcG proteins.
Bibliographical noteFunding Information:
We are grateful to Gary Struhl for providing esc genomic clones, mutant stocks, information about esc rescue constructs and advice. We thank Thomas Gutjahr and Markus No11f or sharing their genomic sequence of the esc gene prior to publication. We thank Madeline Serr and Tom Hays for the loan of a developmental Northern blot. We thank Ellen Miller for performing some of the DNA sequencing runs and Angela Brienzo and Maria Danos for generating some of the esc subclones used in this work. We thank Tom Hays and Ann Rougvie for discussions and critical comments on the manuscript. We also appreciate Ann’s help with late-night database searches. We thank Welcome Bender for providing a home for the initiation phase of this project. This work was supported by NSF grant IBN-9304936 and a University of Minnesota McKnight Land-Grant Professorship to J.S. D.B. was supportedi n part by NIH training grant GM07323.
- Anterior-posterior axis
- Polycomb group
- extra sex combs