The ACT3 gene and epigenetics

The study of epigenetics is important because it provides insight into differentiation and development. The general model for position effect variegation one of the most well-characterized epigenetic phenomena, is that the spreading of heterochromatin along the chromosome results in gene inactivation, and the state of the chromatin structure is inherited, and thus the transcriptional state is inherited. act3-dependent variegation is a new type of epigenetics. The ACT3 gene is an essential gene that encodes an action-like protein. Mutations in ACT3 show a variegated phenotype when his-4delta-ADE2 is the reporter. Two distinct transcriptional states (ON and OFF) were shown to exist in act3 mutants. In this study, act3 temperature sensitive mutant alleles were screen from an act3mutant library. Several mutant alleles were identified and sequenced. One mutant allele has two amino acid substitutions, one of them is in the unique region of ACT3. They were further isolated into two subclones. act3 temperature sensitive mutant strains were constructed by gene replacement. They provide important tools for further study of the ACT3 gene. Another interesting result was obtained in the Gal4p-DBD-Act3p tethering assay. When Act3p was targeted at the telomere, it derepresses telomeric silencing, an effect which is opposite to Sir3p and Sir4p. It might shed some light on the possible function of Act3p.