PcG Transcription Factor Family
Polycomb group (PcG) proteins maintain silencing at target loci in higher eukaryotes
but recent evidence suggests that about half of these proteins are also required for
maintenance of activation at homeotic loci.
The best-studied proteins required for the maintenance but not initiation of repression
of target loci are encoded by genes of the Polycomb group (PcG). PcG mutants exhibit
posterior transformations in embryos and adults caused by derepression of homeotic loci
in flies [1], and in vertebrates [2]. In addition, PcG genes regulate non-homeotic
targets. In contrast, proteins of the trithorax group (trxG) are required for
maintenance but not initiation of activation of homeotic loci [3]. Many genes in the
trxG were identified because they suppress phenotypes of PcG mutations, suggesting that
the trxG proteins act antagonistically to PcG proteins [4]. Structural analysis of PcG
and trxG response elements shows that the elements required for trxG-dependent
activation and PcG-dependent repression are separable but within 30¨C40 bp of each
other. This intermingling of elements required for activation and repression in DNA
sequences previously termed PcG response elements (PREs) or trxG response elements
(TREs) leads us to propose that DNA sequences required for maintenance of gene
regulation be named ¡®maintenance elements¡¯ in recognition of their dual function. How
maintenance of gene expression is achieved is unknown at present but new evidence
supports the idea that there may be overlap between mechanisms of PcG and trxG
modification of chromatin and the chromatin condensation that occurs prior to mitosis.
Notes: PcG family is missed in PlnTFDB.
9 predicted putative PcG sequences,
blast HSP, and multiple sequence alignment in
Soy - TFKB.
24 PcG protein
and DNA
sequences with
annotations for soybean in PlantTFDB. Most are partial sequences.
Last updated by Dr. Jeff Chen on May 23, 2009.