Xin Bi

Biography

"Xin Bi, Professor, In eukaryotic organisms chromatin plays a key role in the highly efficient regulation of gene expression. The genome is organized into discrete structural and functional chromatin domains with different potentials for gene expression. Our major goal is to understand the mechanisms underlying the establishment and maintenance of genomic domains in the highly tractably yeast model system by addressing the following questions. How do silencers initiate the formation of transcriptionally silent chromatin? Silencers are small regulatory sequences flanking HML and HMR in yeast that are responsible for the initiation of formation of a special silent chromatin across these loci. An outstanding question concerning silencer function is whether they act in an orientation-dependent or –independent fashion. We have recently demonstrated that a silencer is intrinsically unidirectional but its genomic context can regulate its directionality. We are examining cis-acting DNA elements and trans-acting protein factors that contribute to the determination of the directionality of silencers. How do barriers block the propagation of silent chromatin? The Sir complex is an integral part of silent chromatin. It is recruited to the silencers during the initiation of formation of silent chromatin. Sir complexes have the ability to spread along the chromatin fiber in a step-by-step fashion thereby encroaching upon transcriptionally active chromatin. This poses the question of how an active chromatin domain is protected from adjacent silent chromatin. We and others have identified various special sequences referred to as barrier elements that could block the spread of silent chromatin. Barriers exist near the silent HM loci but the mechanisms of their functions have not been resolved. We are investigating how these elements restrict silent chromatin to limited domains."

Research Interest

Epigenetic regulation of eukaryotic gene expression; Structural and functional domains of the genome; Chromatin boundary elements; Gene silencing; DNA damage repair and tolerance