In many organisms, repetitive DNA serves as a trigger for gene silencing. However, some gene expression is observed from repetitive genomic regions such as heterochromatin, suggesting mechanisms exist to modulate the silencing effects. From a genetic screen in C. elegans, we have identified mutations in two genes important for expression of repetitive sequences:
lex-1 and
tam-1. Here we show that
lex-1 encodes a protein containing an ATPase domain and a bromodomain. LEX-1 is similar to the yeast Yta7 protein, which maintains boundaries between silenced and active chromatin.
tam-1 has previously been shown to encode a RING finger/B-box protein that modulates gene expression from repetitive DNA. We find that
lex-1, like
tam-1, acts as a class B synthetic multivulva (synMuv) gene. However, since
lex-1 and
tam-1 mutants have normal P granule localization, it suggests they act through a mechanism distinct from other class B synMuvs. We observe intragenic (interallelic) complementation with
lex-1 and a genetic interaction between
lex-1 and
tam-1, data consistent with the idea that the gene products function in the same biological process, perhaps as part of a protein complex. We propose that LEX-1 and TAM-1 function together to influence chromatin structure and to promote expression from repetitive sequences.